Error in %trim BIF with V5R3?

I am working with a customer who it appears seems to have a
problem with the %trim BIF.

The statemenat is:

C                   eval      CatPath = %trim(CatPath) +
C                                       'cat=' +
C
                                      %trim(%editc(CatArr(i):'Z'))
+
C                                       '&'

On my V5R2 machine and some other V5R3 machines it works
great, but on this particular V5R3 machine it's like the
%trim BIF doesn't do anything.

He gets:
cat=100     &cat=ACE     &

It should be:
 
cat=100&cat=ACE&

Very weird.