This file provokes a bug.
This is the log file that proves it.
\setmainlanguage not even needed to trigger that bug!  That’s nasty.
Copying polyglossia.sty as pgwork.sty to find by trial-and-error.
Starting debug session.
Compilation still failing.
Still failing in the same way.
OK, the problem is not in Polyglossia’s code ...
Clearly not.
Working with fontspec now.
Starting work on fontspec.
Fontspec still failing.
Not failing any more without fontspec-patches!  Let’s work on that.
Working on fontspec-patches now.
fpwork almost empty; problem still happening.
... and now still.
Problem disappears when removing fixltx2e.
Working on fixltx2e now.
Forget style file itself.
Getting close to the actual problem.