No, I just installed Max' CustomUI.
As in the first Post described:

"Snapshot
-------------
With this addon you can make a snapshot of last clicked viewport.
Resolution is fixed: 1600x1200
Left click - grid is visible
Right click - grid is hidden
Shift + click = resolution x 2
Ctrl + Shift + click = resolution x 3
Snapshots will be saved to "snapshots" directory."

LeftClick and RightClick on the button work fine.
Combination with Shift or Ctrl+Shift works not and my Backgroundcolor stays white.