PuTTY bug win-jumplist-trouble

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Various people have reported that the Windows 'jump list' features, which maintain a list of recently used sessions (and optionally 'pinned' sessions) accessible via the taskbar button and/or Start Menu, have been broken in various ways since the 0.68 release.

There's a fair amount of evidence that this was triggered by our fix for needs-removeable-media. This fix involved changing how PuTTY identifies itself to Windows for the purposes of storing recent session information (using SetCurrentProcessExplicitAppUserModelID() where previously we were doing nothing). That fix didn't make any provision for migrating any existing stored information; in our pre-release testing, we saw some transitory anomalies from this, but it seemed to work itself out without forgetting recently used sessions, suggesting that Windows can somehow manage the migration itself at least under some circumstances. However, others have seen more permanent effects.

We suspect the exact symptoms seen may depend on the exact history of which versions of PuTTY were run when by what exact means, and/or which flavour of installers were installed/uninstalled/upgraded in what order. Which makes investigating this systematically rather tricky.

If anyone has deep knowledge of how Windows jump list storage works (particularly with respect to how applications are identified) and can suggest ways to mitigate this in future releases without making things worse, that would be helpful.

Reported symptoms:

• The PuTTY shortcut on the Start Menu, which normally has a right-arrow leading to a list of recent and optionally pinned sessions, does not do so.
  • This at least we have some sort of explanation for; we should have made the PuTTY shortcuts created by the installer reference the same AppUserModelID as the PuTTY executable sets at runtime. We have rectified this in the post-0.68 snapshot installers (4c67f0b06).
  • However, in a test on Windows 7, we found that the shortcut did get its list of saved sessions back after a while with no such care taken. Not sure how that happened; I suppose I did launch PuTTY from the Start Menu at some point in the proceedings, so maybe Windows went "aha, this shortcut launches an executable with this AppUserModelID, I shall remember that for next time".
  • One user suggests that the problem only happens if you uninstall 0.67 and then install 0.68 (with any installer); if you upgrade from the 0.67 to the 0.68 exe uninstaller without uninstalling, the issue is not seen.
• Ending up with two PuTTY icons on the taskbar; one permanent 'pinned' icon, and one for the running session. The 'pinned' icon, which would normally have a list of recent or pinned sessions, does not, so is not very useful.
  • But others report that while you can end up with two different icons, they behave sensibly.
• Recent sessions appear, but the 'pin' icon doesn't do anything (demo video). Windows 10, 64-bit.
  • Another user hints that this kind of brokenness (and also broken 'Remove from this list' functionality) might be correlated with the Windows version: broken on 'Windows 10 1607 (Redstone 1 / Anniversary Update)', not broken on Windows 7/8.1/'Windows 10 1511 (Threshold 2)', and affecting both 0.67 and 0.68, although it's not clear what the installation history was so maybe merely having had a new version installed at some point causes permanent confusion.
• PuTTY's taskbar icon is a generic blank-page sort of icon rather than the usual blue-and-yellow PuTTY icon. Has no "Pin this program to the taskbar" option. Other options ("Run Pageant", recent sessions) are present and work. PuTTY icon appears in Alt-Tab. (Observed on Windows 7 with 0.71.)
• One person reported that when they ran the PuTTY 0.71 MSI installer to upgrade their 0.70 installation (on Win 7 Pro SP1 64-bit), they got this error from the installer:

  Warning 1946.Property '{9F4C2855-9F79-4B39-A8D0-E1D42DE1D5F3}, 5' for shortcut 'PuTTY (64-bit).lnk' could not be set.

  (that GUID comes from the MSI installer.wxs script), and after that they suffered the kind of problems described here, which sorted themselves out after using PuTTY to connect to a server. This may be a clue.
• Cosmetic: the way PuTTY identifies itself on the taskbar menu item that launches the executable without arguments seems to randomly fluctuate between 'PuTTY' and 'SSH, Telnet and Rlogin client' (the FileDescription in the resources). This doesn't obviously hurt anything, but may be a clue.

Anyone investigating or suffering from this may be interested to know that the putty -cleanup option requests Windows to delete its stored information about recent/pinned sessions. We make no attempt to account for different versions of PuTTY's information being stored in different places; so running this command with PuTTY 0.67 or earlier presumably deletes pre-ExplicitAppUserModelID information, and running it with PuTTY 0.68 or later deletes information identified the new way. Note that this option also deletes all your saved sessions and host keys; while you can be more selective by saving and restoring HKEY_CURRENT_USER\Software\SimonTatham\PuTTY using REGEDIT, you probably shouldn't try this unless you're confident, or don't mind losing this information. (People investigating the registry should note that the Jumplist key in this registry location is not the storage under discussion here; it is a separate record that PuTTY maintains because the Windows storage is write-only, and hasn't moved between versions. The storage affected by ExplicitAppUserModelID is maintained elsewhere by Windows and we don't know where it is.)