When a desktop or a toolbar applet crashes, it takes entire process down with it. When this happens, Maemo may disable offending applet. I can't remember how it goes exactly, but my guess is that if maemo-desktop can't figure out which applet crashed, it simply reverts to system defaults. In any case I'm fairly certain that you can blame third party applets.

Writing desktop applets is quite different from ordinary applications because the applets are not run as separate processes. When you close an application, allocated resources are automatically freed, so leaking file descriptors or memory isn't that critical. When you disable an applet, you simply stop running the code, and all resources that are not manually freed, are still allocated. The simpliest way to make an applet to "crash" is to have it leak memory. Sooner or later the process is OOM killed, and entire desktop is restarted.