If this stops after you disable remote events by pasting: /remote off
and then re-starts after you enable them by pasting: /remote on
then this is almost certainly a script doing this, and you would just need to discover which one is doing that.
If it still happens while remote events are disabled, it's possible this could be caused by a DLL. You can see which dll's are currently loaded inside mIRC by pasting the following command:
//var %i 1 | while ($dll(%i)) { echo -a %i : $v1 | inc %i }