No, I don't think that's right. The Erase function is supposed to return the card to the fully erased state.
A fancy camera does that too - so stills and video can be written in real time without the need to pre-erase the flash. I've confirmed with my Canon DSLR's "low level" format that it does exactly that on the full-size 1GB card I normally use in it. However, it does not erase the little microSD card. So the problem is almost certainly that the card doesn't execute the erase command properly, but just pretends to. It is a no-name card.
So I just did the SDformatter example Erase on an 8GB Transcend microSD card, and it worked perfectly. So to me that confirms the little card is the problem.