Hoho, personal think, the problem may not directly related to Alcohol.... becase when I encountered this problem, I do not have Alcohol installed. This problem I found at the first time when fansub groups start releasing .mkv files and I tried upgrading the Vobsub from v2.23 to higher version..... but..... maybe may still has a potential to cause.
PS: I'm not talking about WINRAR, but the "unrar.ax" from Vobsub pack. Or, whatever, the ".ax" from upgrade Vobsub version v2.25 above.
Another thought of root cause..... WIN Service Pack!!! If not only English-OS has the same problem but Chinese-OS too.
To 雨过天晴 :
If you still want to keep v2.29 in PC to watch .MKV, only a quick "By Pass" solution is copy archived files from CD/DVD-R to HDD and watch them from HDD..... at least, when files stores at HDD and play, no problem at all...... (don't ask me why... becase I don't know either)..... that is why I call it "By Pass" not a "Fix" solution.... ;)
Do more research and testing..... hope to have solution soon....