NTFS Filename Restriction

[Benjamin]

I have a confusing problem with a windows server 2003. The server is used as
a file server. All volumes use ntfs. There is one share that started to
behave unexspected. In this share there is on folder containing about 1.400
other subdirectories with about 7.200 files.
All went well for several month. The trouble started some days ago.
In some new created subdirectories it is not possible to use filenames
longer than 39 chars.
I can not see why? There should be a restriction of any kind in ntfs, as far
as I know.