I think this should be in Feature Suggestions. It's not a bug, it's intended to work this way. We just need an extra checkbox like "Match whole word only" in Highlight Add dialog.

In the meantime, you can put %z instead of z in the Highlight list and the following code in Remote:
Code:
on ^*:text:*z*:*: if $istok($strip($1-),z,32) { set -u1 %z $1- }

/.timerQ 1 0 echo /.timerQ 1 0 $timer(Q).com