Seen something similar in the bug database but dated from February and it's still in the current release.

The code under ext/bz2 has at least two bugs:

+ bzread without a length returns a string that is not '\0' terminated. On systems where (e)malloc returns a initialized memory it works fine, but when the memory is not initialized it breaks.
A quick fix is to use ecalloc instead of emalloc

+ bzcompress (and perhaps bzuncompress ?) uses a size argument for the second parameter of libz2's BZ2_bzBuffToBuffCompress function.
This parameter is NEVER initialized, it should be initialized to dest_len.