It applies to both SSL and non-SSL connections.
Hmm. I have been dealing with this issue since mIRC introduced SSL support and have never once seen this happen on an unencrypted connection, no matter how I disconnected it (usually by clicking the disconnect toolbar button or closing mIRC using the X in the upper right corner).
Using SSL on the other hand, I can pretty much reproduce this issue at will: When I terminate such a connection in the ways described above, "Input/output error" shows up about 9 times out of 10. This is why I've always thought it must be related to SSL being "in between" things and possibly not forwarding the quitmsg correctly.
Is there really nothing that can be done except use /quit to close secure connections? I'd be glad to help track this down if there's anything I can do/test.
