Hey. For those among you, who have actually updated to RC2, here is a little fix, if you like manual patchwork. If you prefer the easy way, just download RC3 here. Apologies!
This fix is yet another issue that can be traced to the NT script interpreter. The problem is the wrong handling of string substitution with empty strings. In case of an empty string, the substitution string is wrongly considered to be the actual content to set. Of course with unpleasant consequences.
Anyway, if you like the manual fix, search for:
and replace it with
if not "" == "%PATH_EXTSHORT%" set PATH_EXTSHORT=%PATH_EXTSHORT:~0,4%