I'm sure PHP doesn't affect any of system functions, including stat().
You get what your stat() returns -> not PHP problem.

I have to agree with the original poster.  Running php 5.2.13 Under Gentoo I have problems with is_dir() on CIFS shares with 2.6.31 and 2.6.32.  On a machine I have running 2.6.30 I don't see the issue.  Here's a CIFS mounted directory that reports is_dir() as false even though chdir() reports true:

php -r 'var_dump(is_dir("/home/tom/mount/sql"));'
bool(false)

php -r 'var_dump(chdir("/home/tom/mount/sql"));'
bool(true)

Here's the equivalent in perl that reports true:

perl -e '(-d "/home/tom/mount/sql") && print "OK\n"'
OK

ls -ald /home/tom/mount/sql
drwxr-xr-x 1 tom tom 0 Apr 28  2008 /home/tom/mount/sql

That's a windows share mounted as administrator of the windows machine. While this may be caused somehow by CIFS changes in the kernel, there truely is something ugly going on here and it's caused me some serious problems.

Tom

I just found a blog post (which I had to dredge out of the google cache) where someone figured this out.  The CIFS mount is now apparently using the serverino option by default.  In the case of Windows shares this appears to be resulting in huge inode numbers which are causing is_dir() to report false.  Using the noserverino option prevents this.  Scary stuff.

Just spent 5 hours trying to figure out an issue that was caused by this bugger... 
If PERL handles this case properly then there must be a small issue with PHP's 
implementation. I'm happy to attempt to provide a patch if someone can point me in 
the proper direction.

I could be wrong, but since this appears to be related to the large inode numbers caused by the newer CIFS code defaulting to serverino, I'll bet the 32 bit integer limit may be part of this issue.  If so, you're no more likely to fix this than, for example, the 2GB limit with filesize().

It'd be interesting to know if this can be reproduced with 64 php builds.

I've stuck with my previous work-around of using noserverino with my CIFS mounts.