$zu(96,9) Not working

Suppose you have routine ^A loaded in your partition in programmer mode and you call routine ^B. Routine ^B finds the value of $ZU(96,9) which should be the calling routine.

But $ZU(96,9) now returns null, as does $SYSTEM.Process.CallingRoutine()

Works on 2018.1.7 but not 2018.1.8

$ROLES= %All on both systems

More precisely I have line label ZZPP in ^%ZLANGC00 which needs to identify the original routine in the partition and do some work on it. When I type ZZPP I get nothing on the later version. Here's the line of code:

ZZPP New RTN Set RTN=$ZU(96,9) QUIT:RTN=""  WRITE !,$T(+1^@RTN)

If I add a line label zzpp to my calling routine that reads "zzpp ZZPP  QUIT" and then "DO zzpp" while the routine is loaded, it works.

ZL A ZZPP  ; should work but doesn't