Comment 2 for bug 160483

Fixed in revision 996.

Just in case you're interested:
    - The real reason was in the register allocator, where one live
      variable (the memmory size of the bytevector) was not marked live
      across the call to do-overflow. When the overflow returned, the
      value of that variable (which was in the %ebx register) was
      trashed, leading to an incorrect bump in the allocation pointer.
    - Note to self, never blame anything on cache coherency again!