Now this might be some funky windows-help cache issue, but I cleared what I thought was the cache, and it didn't help.

Executing '/help $tip', or just searching the help for '$tip', brings up an error whilst accessing the help item:

Originally Posted By: HelpFile
Internet Explorer Script Error
An error has occured in the script on this page
Line: 87
Char 50
Error: Expected ';'
Code: 0
URL: mk:@MSITStore:C:\Program%20Files\mIRC\mirc.chm::/tips.htm
Do you want to continue running scripts on this page?
Yes / No

Clicking either advances to the page correctly.