TYPO3 Core

I can confirm this. It is based on t3lib_basicfilefunc::cleanDirectoryName which removes also dots of directory names. I think only dots at the beginning of a directory name e.g. ".svn" or ".." should be removed.
See the attached (fast) patch and check if the new preg_match is correct.

I think your regex is wrong. According to the function header, it should remove "all dots, slashes and spaces after a path". However, since the dots are obviously a mistake by design, this is the only thing that should be changed in the regex. Directory names with a dot at the beginning are still allowed, it just means they are hidden on Unix systems.

See attached patch.

Okay, if this only concerns the end of a string, it looks good.
+1 on reading the patch

This issue is still actual.

I created a Folder called 'Dot.', which was displayed as 'Dot.' in the fileadmin of T3 and the OS filesystem. Nothing happens If i click to the folder. If i want to rename the folder, the same behavior as in bug description appears.

Looks like that T3 create a folder with a dot and after that its not able to found this folder on the OS filesystem.

Need to cut the dot before save the folder to OS filesystem.

Figured out with Kubuntu Linux 4.08

With current trunk those directories can no longer be created; no matter if on a UTF-8 filesystem or not.