Confirmed. Also relevant:
CHANMODES=beIqa,kfL,lj,psmntirRcOAQKVCuzNSMTGHFEB
From my tests, it appears that mIRC is interpretting "[5j#i1,4k#K5,4n#N2,4t#b]:10" as two tokens instead of one. I think this shows the problem clearly:
[19:50:17] <@drum_test1> @+drum_test1 @+drum_test2
[19:50:22] * drum_test1 sets mode: +f [5j#i1,4k#K5,4n#N2,4t#b]:10
[19:50:55] * drum_test1 sets mode: -fvo [5j#i1,4k#K5,4n#N2,4t#b]:10 drum_test1 drum_test2
[19:52:20] <+drum_test1> +drum_test1 @+drum_test2
When I am speaking, I am using: //say $nick(#,drum_test1).pnick $nick(#,drum_test2).pnick
Based on this, mIRC appears to be pairing the third mode change (-o) with 'drum_test1' instead of 'drum_test2', implying that it believes there are two tokens in front of 'drum_test1'.
As an aside for xmrfunny1x: until this is fixed, you can force mIRC to correct the issue when chanmodes become desynced by typing /names #channel.