CCleaner keeps deleting .TIF association

On multiple machines we have selected to not scan for Unused File Extensions. We haven't had this issue for six months or more and it's coming back again. In each person's CCleaner preferences, the Unused File Extensions options is unchecked. These users open online .TIF files everyday, so I'm unsure as to why Windows would be telling CCleaner that the file extension is rarely used and why CCleaner would delete it out when the option is unchecked.

Any ideas?

Read the last part of this post on how to input a registry exclusion.