Dropbox corrupts Windows 10 Start Menu

I have the same issue as well, with the same behaviors.
Dropbox autoupdates; bug is back, uninstall dropbox, bug is gone, install dropbox all is fine, dropbox autoupdates, bug is back, uninstall dropbox, bug is gone, install dropbox all is fine, dropbox autoupdates, bug is back... etc ad nauseam

This has been happening to me too—not just for pinned folders on the start menu but for any folder I open from the start menu (even by manually typing it in) except for the main drive. It appears to be a Windows bug that's being exacerbated by an annoying feature in Dropbox that isn't configurable. I only thought to consider Dropbox the culprit because it didn't start until after I recently installed Dropbox on my new computer after having left it alone for a while.

Here's the discussion on Microsoft's answers forum (see WillCampbell7's response near the beginning of page 3, since Microsoft has no permalinks):

Microsoft discussion of start menu not closing 

The problem therefore appears to be the "Send a copy" shell extension that Dropbox adds, which is interacting with a known Windows bug.

This is a request another user made to remove the context menu items:

https://www.dropboxforum.com/t5/Apps-and-Installations/Can-I-delete-the-Dropbox-context-menu-items-that-appear-when-I/td-p/642181

There appear to be two solutions. One is for Dropbox to either make the context menu item removable like it should be. (I don't know why certain shell extensions have an issue and others don't. That's something Dropbox should investigate if possible.) The other is to block the shell extensions entirely, which I haven't tried yet but I intend to as it appears to be the only workaround for now. I can't keep having folders opening in the background.

Okay, update: I blocked the shell extension and restarted Explorer. Oddly, the context menu still appears, but the bug with the start menu has gone away (at least for now). Following instructions similar to those on the aforementioned Microsoft discussion:

1) Open the registry editor.

2) Go to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Shell Extensions\Blocked (create the Blocked key if necessary)

3) Create a new string value "{ECD97DE5-3C8F-4ACB-AEEE-CCAB78F7711C}", and give it a value of "DropboxExt".

4) Go to the Task Manager's details tab, right-click explorer.exe, end task.

5) Still in Task Manager, go to File | Run and type explorer.exe to restart the taskbar.

After I did this the start menu was behaving properly again. If it fails to keep doing so I'll follow up.

Unfortunately the problem has returned. I still think Dropbox is the primary reason for it, because it didn't start until I installed Dropbox. There are other shell extensions Dropbox adds that maybe need to be disabled, but unlike the context menu extension I don't know if it's as safe.

I am however still seeing "Send a Copy..." in my context menu, so it's also possible that the instructions I was given for disabling certain shell extensions are simply incomplete.

Hi again, JCplusULTRA. I’ve sent you an email. Reply back to me, when you can, please.

I should add I just had this happen with a pinned application when I started it in administrator mode as well, by right-clicking it on the start menu. Probably the same thing is causing it. Dropbox has multiple shell extensions though so I wouldn't necessarily rule out that there's more besides the context menu shell extension. I haven't tried blocking the extension yet, though.

Sorry to hear about this, LummoxJR and thanks for all the info you gathered.

Just to confirm, does the issue go away when the Dropbox app is closed or uninstalled?

@Hannah I haven't uninstalled Dropbox or exited the app. I did, today, change the ForegroundFlashCount registry value described here:

https://answers.microsoft.com/en-us/windows/forum/windows_7-performance/windows-7-explorer-window-does-not-appear-in-front/1199682e-2415-4a7a-bf21-f57a972122ee?page=1

Right after starting up my computer I had the issue recur, so I went into the registry and changed ForegroundFlashCount from its value of 7 to the proper default of 3; I don't know how or when it got changed to 7. Immediately afterward, even without restarting explorer.exe, the problem went away.

I'm not certain at this point if I've licked the problem or if it'll return in a future session. All I can say is that it never happened at all until about when I installed Dropbox, and I had no other installations or updates around that time that would explain the change. This appears to be a problem a lot of users have had with Windows and is, ultimately, a Windows bug, but it seems the Dropbox installation is what kicked it off for me.

Thanks for keeping us updated on your experience and what has worked for you, LummoxJR.

Hopefully, this will be useful for other users experiencing this issue as well.

If the issue does return, though, let us know.

The problem resurfaced on the next session and doesn't go away when closing Dropbox. It appears to be a very weird intermittent Windows issue. I don't know why it started with installing Dropbox, though.