Magic 12 - Show bug report

=========================================================
 THESE ARE NOT BUGS IN DOSBOX, BUT NOTED
=========================================================

Memory corruption bugs:
 - If UMBs are enabled, Show will cause an "MCB list corrupted"
   message after the demo has run, when you run certain other programs
   like MEM.COM. Apparently Show overwrites 2 bytes in the
   last MCB below 640KB at segment 0x9FFF sometime during the demo.
   The 2 bytes written happen to stomp on the upper 8 bits of some
   other field and the lower 8 bits of the segment size field. Once
   the segment size is corrupted, the MCB no longer points to the
   first block in UMB, and DOSBox detects this as an "MCB list
   corrupted" error.

   Workaround:

   You can avoid this crash/memory corruption by setting 'dos mem limit'
   to a value less than 640 (such as 'dos mem limit=639') to mark off
   the last 1KB of lower conventional memory as off-limits. If the demo
   corrupts the bytes at segment 0x9FFF, it will have no effect and
   DOSBox will no longer crash with "MCB list corrupted". It's possible
   nobody ever caught the bug because most BIOSes by that point had
   started taking the top 1KB under 640KB for the EBDA (extended BIOS
   data area) and the corruption merely affected the unused trailing
   end of it.

==========================================================
 THESE BUGS ARE FIXED
==========================================================

VGA raster bugs:
 - 18-bit RGB highcolor hacked modes work except for minor errors
   in linewise rendering that cause visible "stripes" in the output
   (but only if the cycles count is greater than about 9000).

