problem:
Whenever I use the /server command with a server name, but without -m, log files of all the channels joined on the previous network are moved to the log directory of the new network.

e.g. /server irc.dal.net <-- will move all channel logs from the prior network [the one that this /server command quits] to DALNet's logging directory.

configuration:
I'm running mIRC 6.20, set to:
* automatically log both channels and queries [IRC > Logging];
* add timestamps, strip codes [IRC > Logging];
* make a folder for each network, and logs dated by month [IRC > Logging];
* keep channels open [IRC];
* hide the switchbar, show the treebar [View > Switchbar/Treebar].

reproducing the problem:
* configure your mIRC as in the configuration section;
* connect to a server, then join a couple of channels on that server (e.g. //server irc.efnet.org | join #coffee,#anna,#whatever_else);
* connect to another server (e.g. /server irc.dal.net).
Now look in your EFNet logging directory; there should be logs, but there aren't. And since you haven't joined any channel on DALNet, looking in its logging directory should show no logs, but your prior EFNet logs are in there.

Using the -m option eliminates the problem completely, but leaves me having to /quit the first server.