Are you using the spellchecker in the "description" box? If you don't see it then you don't have the full edit box opened. I don't know if that can happen but there is a spell checker there.
As for the "detail" boxes, I don't recall a spellchecker....but I may just be not remembering it.
If you are in Firefox it should underline the mispelled words anywhere. I prefer to do the listing with FF, but I like to drag and drop pics so I keep IE open to use it when getting the pics.
My spellchecker on the Google toolbar will not spell check Auctiva anywhere!
Hope I'm responding to your question. I am new and don't know much yet.