utl_file on mapped drive?

UTL_FILE.FOPEN fails with an INVALID_OPERATION exception on the server when using a drive mapping, even if that drive mapping has been specified as a utl_file_dir in the init.ora.

Is this a bug?

Some further details:
The server has a dir C:\X\Y
and a mapping of T: pointing to C:\X
I can Dir T:\Y OK.
I have utl_file_dir=T:\Y
Utl_file works on C:\X\Y but not on T:\Y

any thoughts?
Steve
p.s
This might sound odd, but I need a common view of a mapped drive between client and server so that get_file_name() builtin from forms5 can invoke a loadit() procedure for a chosen file.

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