Some applications don't themselves link against libpthread, but then load plugins which do link against libpthread. This means internally switching from single-threading to multi-threading, which is not yet supported by our libpthread, and results in errors such as:
./pthread/../sysdeps/generic/pt-mutex-timedlock.c:70: __pthread_mutex_timedlock_internal: Assertion `__pthread_threads' failed.
This can be worked around by making the application link against libpthread (i.e. not only the plugin, but also the main binary), or without recompiling by explicitly pre-loading libpthread, for example:
$ LD_PRELOAD=/lib/i386-gnu/libpthread.so.0.3 [application]