Yeah, this bug surfaced about a year ago, and nothing's been done about it.

It seems to vary from time to time what could be done in the eBay seller tools -- last I sold something, I was not able to complete making the listing from Safari. I had to use Firefox.
I have no idea why neither eBay nor Apple has done anything about it, given eBay's popularity (it isn't some random piddly website). Actually, my guess is that Apple will tell you that they support standards and eBay's site fails to comply with the standards. eBay will probably tell you that they don't support Safari at this time, which of course is not informative.
As far as a solution, probably the most palatable one at this time is to keep Firefox on your computer as a backup browser, and use it for this purpose. Everything except making a seller listing seems to work in eBay on Safari, and I personally don't really need to switch into Firefox for too much else at this point.
If you have the energy, it would be good also to e-mail eBay and complain about it. Remind them that Apple customers tend to have bigger wallets and tend to be more willing to spend their money on good products. Working on Apple software only makes sense for eBay.