OK, with a fresh install of 621, ive got another person to do this same happened to him.

If you have the mirc 6.21 help file open mirc and type /help $ial a dialog will popup with 2 $ial options keep the dialog open click back into mirc and mirc is now frozen

Confirmed.

Although I would class this as an annoyance rather than a bug. (i.e. It's not the software working incorrectly, per se)

BTW, it's not necessary to already have a help file open. It will do it directly from /help $ial or any other parameter that gives that "disambiguation dialogue" (for lack of a more snazzy term for it)

I think that read as:

Oops. I slipped in an extra "open". Apologies

This appears to be a Windows HtmlHelp issue. When the Windows HtmlHelp system displays the "Topics Found" dialog, the calling application is frozen until the user selects a topic and closes the dialog. There does not appear to be a way around this.

Yeah this sucks.