zsh function does dot get back in foreground

[Pol <xpol@xxxxxxxxxxxx>]

I am using the function 

m () {
        $PAGER $PAGEROPTS $*
}


to view files.
As i view single files, it is ok, but as i use that fuction to view the
'diff' command out put, e.g.:
  
% diff file1 file2 |m 

i cannot recover the output after the 'm' function has been put in the 
beckground. 
Entering 
% fg
seems to reget 'm' in foreground, but 'diff' out is not displayed on
terminal any more. 
The only way out is to kill 'm'.

If 'more' or 'less' is used instead, everything is ok.

What is wrong?

thank you 

--
Pol