Command Button moving from right to left

I'm sure this is a no brainer, but for some reason it escapes me (perhaps due to lack of brain).
I have an Excel 07 spreadsheet with several tabs, buttons, and macros. At the top of one of those tabs, generally aligned with Column R, is a Command Button.
When the user has completed all the procedures, he/she clicks another command button, which removes all the data from the workbook (deleting rows/columns instead of clearing them) and rebuilds all the named ranges.

The button in question gradually moves to the left, not aligned with any cells or columns, mind you, but just a bit at a time every time the data is cleared out.

I have the button format set to "do not move or size with cells" and the properties
AutoSize = False
Locked = True
Placement = 3 (no idea what that means and can't find a good description)

Anything obvious that I'm missing?

Thanks in advance
JP (smartest idiot around)