Well, you'll want to check for yourself, as several things have been reported to throw of the Chargemaster and other scales.
Fluorescent lights, drafts, static, cell phones.
I haven't personally tested static but I have tested drafts, CFLs and cell phones. None have any effect on my scale, unless I blow on it so hard that it blows the powder away, which seems a little irrelevant.
If I were you, I'd wipe down that cover with a used dryer sheet and see if the problem goes away.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.