still running old version of Tor Button after upgrading TBB in-place

I've been upgrading TBB by untarring the new one over my old one, to preserve my preferences and bookmarks. I've heard this is not recommended, but I haven't heard a better way to accomplish this goal and as I use TBB for everything I'd really like to have my preferences saved.

After upgrading to 3.6.3 I happened to notice I was running an outdated Tor Button. I investigated a bit but have been unable to determine how this happens. But, it is reproducible:

1. Untar and run TBB 3.6.2 (on Linux, in my case)
2. Quit TBB.
3. Untar and run TBB 3.6.3
4. Look at the versions of the extensions (under Tools->Add-ons).

In my case, the Tor Launcher and HTTPS Everywhere are the expected versions (what is listed in the 3.6.3 release notes), NoScript is newer (it auto-updates, apparently) and Tor Button is older. I confirmed that the file at tor-browser_en-US/Data/Browser/profile.default/extensions/torbutton@torproject.org.xpi contains the correct version (1.6.11.0) and I don't see any other tor button files in my tor-browser_en-US, so the old version must be getting cached somewhere.

I suspected this might be related to the fact that the file has an mtime of Jan 1 2000 (which I assume relates to the deterministic builds), but the other extensions which do update have that mtime too.

I was able to get the new version to run by removing the file from the extensions directory, running and quitting TBB, and then placing the file back there.