People still use Windows98?
It appears that the wildcard "?" means "null or matching character", so ".????.rvt" means "one or up to 4 characters before the .rvt", and not "4 characters before the .rvt" as intended. CCleaner appears to work in the same manner as the "dir" command does on XP/Windows2003/Windows2008/W7, and probably uses the same basic API, hence the same functionality. I'll have to look elsewhere for something with regex support to be able to clean out these files, or write something myself ...