I honestly can not say either way if your claims have any merit, while it has annoyed me in the past i have never payed a lot of attention to it because the endless discussions never weild any results.
I do not get it often at all (and i used modes etc all the time), and i think i have seen the error in an ftp program maybe once, in total.
Regardless of the method used in mirc to try and reproduce this (using modes as you say), it does not prove it to be a mirc issue, nor does it disprove it.
I have however just set up a test client to see if a disconnection will occur now that the channel central has been opened, so only time will tell i guess.