Forums Bug Reports does not like folder named IP

tested in mIRC 6.21 and 6.16 and 6.17

//echo -a *** $isdir(c:\test)
*** $false
//mkdir c:\test
//echo -a *** $isdir(c:\test)
*** $true
//mkdir c:\test\ip
* /mkdir: unable to create 'c:\test\ip'
//echo -a *** $isdir(c:\test\ip)
*** $false
//echo -a *** $isdir(c:\test\ip\)
*** $true

This is the only special case i've found where $isdir requires the ending backslash, and it's strange that mkdir does create the c:\test\ip\ subfolder, even though the script bombs with an error message saying it didn't.

I tried with a few other subfolder names like longip or url or version without finding any other foldernames doing the same thing. c:\ip does the same thing.

<<EDIT: using XP >>