I used mIRC for a very long time, upgrade when a new version is released and it works fine with the setting that "#channel=#channel.log".
But it works wrongly after upgraded to 6.21 this Friday and I posted the problem here.
I suppose that it changes "#channel.log" to "logs\#channel.log" from 6.2 to 6.21. But it is not. It should be much earlier version to 6.21.
Then the solution was found when I tested with the old version last night. :>