http://bugs.winehq.org/show_bug.cgi?id=24586
--- Comment #6 from dino dyvazar@numericable.fr 2010-10-02 09:45:33 CDT --- as my .wine is updated from previous release to next one since 6 months or so, and checking windows/system32/ let me see old dlls that can (maybe) conflict with actual 1.3.4, i decide to start with a fresh wine install.
Restarting with fresh 1.3.4, MT5 work fine again, so closing this report now.