There is a consistent failing assertion on 32bit platforms (linux/windows, x86/arm), the Q_ASSERT(testBit(index)); around qv4mm.cpp line 170. You can see it consistently happen in the ecmascript testsuite. It is not a specific test that fails: it takes some amount of test passing before it happens. The testsuite will pass if you disable the assertion.
Note that the affected versions are just a small subset. I've seen this happen for quite some time/releases.