Multiple people touching the same file with ange-ftp

[rgb]

I'm reading in the manual where it says:

Every time Emacs saves a buffer, it first checks the last-modification
date of the existing file on disk to verify that it has not changed
since the file was last visited or saved.

This doesn't happen when I visit a file via ange-ftp.
I'm accessing an unusual host so most of the support I've had to write
myself.  But I don't see anything related to modification timestamps
begin called when I trace the ange-ftp calls so I'm not sure how/what
to modify to make this work.

Does anyone have even the slightest idea where to start looking in
order to add support for this.

Thanks