Re: Error in menu-bar-update-hook: (error Point before start of prope rties)

[Richard Stallman]

    I occasionally see this error in the minibuffer, after which it seems
    menu-bar-update-hook is set to nil.

The reason menu-bar-update-hook is nil is that it was run using
safe_run_hooks.  If the hook gets an error, Emacs wipes out the hook
value, to avoid an infinite repeat of the same error.

The anomaly here is in the original error.  I am not sure whether that
error ought to be possible at all.

How about if you run with a breakpoint at the line in intervals.c
which gets that error?  When you get there, look at the value of POS.
Then examine the existing buffer properties.  You can do that at the
C level, or continue into the Lisp debugger and do it there.