Description:
------------
This seems to be much the same issue as #41518. But, maybe it only occurs when exactly matching a file.

i.e. When using file_exists(), I get an error along the lines of:
PHP Warning:  file_exists(): open_basedir restriction in effect. File(/foo/somefile.php) is not within the allowed path(s): (/foo/somefile.php) in ...

Clearly, the error is wrong, when the allowed path is exactly the same as the file name. If I create the file, then the warning disappears, which proves that it is in the allowed path.