[KevinH]

The only period being replaced is at the beginning of the file extension. Also each potential new id is always checked for uniqueness and made unique before it is used.

Note the filenames themselves do not have to be unique at all as long as their epub relative paths from root are different. So uniqueness does not rely on just the filename.

Do you have a test case opf that illustrates an issue? If so please post it for me to recreate the bug. Or is this only in the abstract case? If the latter, no worries.