The most serious Memtest86+ bug I've discovered so far:

  1. Boot to Memtest86+.
  2. Select test 10 (C - 1 - 3 - 10 - Enter - Enter).

Look at the pattern used: it changes continiously from "00000000" to "ffffffff" and back.

Workaround: before step 2, select test #6 and let it run for a sec.