I had a share called "Accounting" (10 characters). I could see that share from clients (WinXP/2K) but any file would be opened as read-only, despite being writeable from the viewpoint of Windows, the Samba configuration, and the underlying filesystem configuration. I changed the share name to "Acct" and the behavior changed to the expected (writable files). Before changing the share name, I confirm that file locking (either in Samba or on Linux) were not the problem. WinXP and Win2K don't have problems accessing long file names (that I can find) so it looks like this might be a limitation in Samba. I could swear that this bug was not present in 3.0.8 or previous but I'm not able to revert to test it.
please retest against 3.0.21a. I'm a little skepitical about the original bug report only because it doesn't make logical sense to me based on code reviews. Please reopen if you can still reproduce the issue.