svn diff issue: svn confuses files with dirs on hfsplus?

Hi!

I encoutered a weird problem with subversion 1.6.6 & 1.6.9 on a 32 &
64bit Xubuntu 10.04: My working copies are located on a hfsplus
partition which is shared across the Xubuntu Linux and MacOS on my
development machine. For some strange reason, I cannot diff single files
in any working copies on this partition:

$> svn diff somefile
svn: Can't open file 'somefile/.svn/entries': Permission denied

Weirdly, running

$> svn diff

works well, however, and shows a diff of all files as expected.

After checking out the same repository to an ext3 partition, _both_
commands work fine. Based on the error message above, I wonder why
subversion confuses a single file with a directory? Why is it looking
for .svn/entries that does obviously not exist?

hfsplus is case insensitive, but I successfully used subversion on such
a partition for quite a while before. I suppose, the hfsplus partition
is not mounted correctly. These are the mount options I use in my fstab:

UUID=... /media/Data hfsplus users,auto,exec,rw 0 0

Any ideas that might help me solve the problem?

Georg