I added some instrumenting code. When it looks for DLLs, it does the right thing (uses sub vs_config_dir), but 'sub find_mysqld' ignores vs-config completely, and finds the first available one! In this case, I asked for the debug configuration, but it found the first available one which was RelWithDebInfo.

Apart from being incorrect, this can also cause crashes due to inconsistency created between modules.

D:\dev\bzr\mysql-server\maria\mysql-test>mysql-test-run.pl --vs-config=debug --do-test=maria
Logging: D:\dev\bzr\mysql-server\maria\mysql-test\mysql-test-run.pl --vs-config=debug --do-test=maria
== D:/dev/bzr/mysql-server/maria/client/debug/ ==
MySQL Version 5.1.42
Checking supported features...

• SSL connections supported
  == D:/dev/bzr/mysql-server/maria/storage/example/debug/ha_example.dll ==
  Collecting tests...
  vardir: D:/dev/bzr/mysql-server/maria/mysql-test/var
  Checking leftover processes...
  Removing old var directory...
  Creating var directory 'D:/dev/bzr/mysql-server/maria/mysql-test/var'...
  Installing system database...
  Using server port 1606

==============================================================================

TEST RESULT TIME (ms)
------------------------------------------------------------

Found the wrong one!!! D:/dev/bzr/mysql-server/maria/sql/relwithdebinfo/mysqld.exe <--- here.