GKrellM and Mint on laptop, leaving gap when on same edge as Panel

How can I move GKrellM to the desktop edge?

This problem only exists on a Lenovo laptop running Mint 17.2 based on 
Ubuntu 14.04.2 LTS, the screen size is 1024x600, the window manager is xfwm.
gkrellm version 2.3.5-5 is the newest version on the Mint Package Manger 
listing.
By "only exists" I mean this problem does not happen on a desktop 
running Debian 8, and larger screen size, also running xfce.

When I grab GKrellM and drag it around the desktop, it stops from the 
left edge, leaving a gap of 12 pixels.
Suspecting the Panel on the left edge is responsible, I unlock Panel 2, 
and drag it to the right edge. Now GKrellM can be dragged to the left 
edge (lower corner). When I drag Panel 2 back to the left edge (upper 
corner), then GKrellM jumps away from the edge again.

Is there a setting I am overlooking?

Thanks,
Stewart