I've had this problem once, just a few weeks ago. I don't use Handcent or task killers. I had gone into settings and set the maximum texts to 2000, and was somewhere in the 1900s with my girlfriend, not counting the various other text threads I had not yet erased, when I got a new text, and ever single other text was gone.
Before I had changed the settings, I hadn't yet hit the stock 200 max mark yet, so I do not know if it was the settings or not, but felt safe to assume it was. I always instinctively save all pictures or important messages to my SD card and forward them to my email, so I wasn't too upset about losing anything, but did find it awfully peculiar.
After reading geetarspaz's post above, I checked my Messaging settings, and delete old messages is automatically checked, so people who do not want to lose old messages should uncheck that, and will not have to worry about a cap limit either.
Before I had changed the settings, I hadn't yet hit the stock 200 max mark yet, so I do not know if it was the settings or not, but felt safe to assume it was. I always instinctively save all pictures or important messages to my SD card and forward them to my email, so I wasn't too upset about losing anything, but did find it awfully peculiar.
After reading geetarspaz's post above, I checked my Messaging settings, and delete old messages is automatically checked, so people who do not want to lose old messages should uncheck that, and will not have to worry about a cap limit either.