Discovered something of a bug running on my Lumia 900. I am also running the Folders app by Jaxbot (whpFolders.xap) over at Windows Phone Hacker
http://windowsphonehacker.com/articles/folders_for_windows_phone_mango_first_release-10-27-11. If I open Board Express, which is in a Favorites Folder on my Start screen, the background task for Battery Status will be disabled after 10 minutes (I have Battery Status set to record the current battery percentage every 10 minutes vs. every 30), which disables the Live Tile and stops recording battery stats for the graph.
I was able to reproduce this three times today, opening my Favorites Folder, tapping Board Express, going to XDA or WPC, and keeping the screen on for 10 or 11 minutes. Each time I backed out of BoardExpress/Favorites and checked Battery Status, the Tile was disabled. I tried opening Board Express from the Apps menu and could not recreate the problem. I also opened Board Express from my Favorites folder and then tap/held Back to bring up the multi-task view, selected the folder screen and closed it, returning to Board Express for 10+ minutes and the Battery Status background task did not turn off. This only appears to happen when Battery Status tries to run it's background task. Don't know if the same thing would happen if Battery Status were set at 30 minutes.
Note that I have been using the desktop version of Folders since it was first released and Board Express has been in my Favorites folder since then. I access Board Express several times a day and have never experienced the Battery Status app being disabled. The problem started as soon as I uninstalled the desktop version of Folders and installed the latest device version. Pinned the problem down after it happened for a third time this morning. Also note that I only have five active background tasks so that's not an issue.
I tried to recreate the same issue with other apps in my Favorites folder but couldn't. One app only ran locally and the other was a Radar app, that I assume was constantly updating, but maybe not.
I will try to recreate this issue on my Surround to determine if this is device specific. I will post this same info in the Windows Phone Hacker thread. Hope this can get figured out.
UPDATE: I was just able to recreate the exact same issue using my Surround. So this is not device specific.
UPDATE2: Here is an interesting tidbit. If the Battery Meter app is in a tombstone state, you can't launch any app from any Folder (app links in folders). Close Battery Meter app (but still running background task) and all works again. No issues with opening other apps from Start screen or Apps list.
UPDATE3: Here is an update from Jaxbot:
When typing a reply, I figured out what the issue is. Both this app and Battery Meter use DLL Import to load native functions. It has nothing to do with the fact that you're using Board Express, but rather, that Folders is still running in the background, and thus the calls to register the COM are probably failing.
I'll see about switching over to my own library to see if I can clean some of this mess up.
Sorry about that, not something I predicted as an issue.
With the little bit I understand about programming, this makes some sense.