Yup, same thing happens here. It seems both $dllcall and $comcall have this problem. Additionally, it seems $comcall has another problem.
/comopen Excel.application
//echo -a $comcall(test,blah,Visible,3)
Next thing I know, mIRC is completely frozen and requires a ctrl+alt+del. And yes, alias blah exists (echo -a $1-) and if I do the same thing using $com, $com(test,Visible,3) it works perfectly.
And also with $dllcall, imho the alias should NOT be called if the dll didn't return anything. I have a function in a dll called DisplayWarning, it doesn't return anything to mIRC, however I wanted to use $dllcall rather than $dll so that mIRC isn't frozen until the dialog box is closed. Well I have the same blah alias above specified, and for some reason it calls that alias with the parameter being the path to the dll.
Honestly, I'm really starting to wonder, do features actually get tested when they get added to mIRC? It seems as though just about every single new feature has bugs in it. I woulda thought after a year of development, most of the bugs would have been worked out.