Threaded texts in WM 6.1: Completely screwed. :(

[exi]

At some point, it seems that WinMo 6.1 likes to start a new thread for the same person if the text message history with said person gets too long. I wasn't sure if this was a bug of some sort or a "feature", so I changed the text message format to Classic / unthreaded, soft reset, changed back to Threaded, soft reset, and much to my dismay, I noticed that chunks of the message history for several people were missing (including anything sent while the format was still Classic).

How can I force the threading of all messages? I have quite a few on my phone -- somewhere in the neighborhood of 13,000, inbox and sent items included -- but this incomplete history nonsense is completely unnecessary.

Should I just backup my texts with PIMBackup or something similar, delete everything, and restore the backup? Not sure what's going on here, but even left overnight, texts just aren't working the way they should.