Yup, that is the question. Two other players and I all ranked up to Captain some days ago, and we were all quite surprised to find out we can't assign more BOs than as Commander. We were kinda certain we'd get 2 more slots (we have 8 now).
Yeah, I've always thought this was weird since closed beta. Although I'm sitting at RA5 with about 4-5 officers that are basically placeholders/pack mules, I still think it's weird that Lieutenant Commander, Commander, and Rear Admiral all gain additional officer slots while Captain does not.
(Actually, something that annoys me more is the fact that any Fed ship doesn't have any 'off-career' (Sci career would be Eng & Tac, Tac career would be Eng & Sci, Eng career would be Sci & Tac) officer stations above the Lieutenant rank. While I can understand the reasoning, (for balance sake, would have too many officer ability options, etc etc) it still doesn't seem right to me that my Tactical officer can only use a Lieutenant-ranked station aboard my Reconnaissance Science Vessel (Tier 5 - RA level). Meh, that's really off-topic here, though.)
I wonder if they'll ever up the officer limit to 12 (and make Captain 10 and Admiral 12), or (more likely) keep it the way it is. Actually, I have plenty of officers (for my tastes), so I wouldn't mind maybe 9 at Captain and 10 at Admiral. (Or keeping the 8 at Captain and 10 at Admiral works for me)
I was also under the impression that a Captain gets 10 and RA 12... Feels indeed weird. I sold most of the reward BOs or gave them to alts and other players, but I had kept 2 with traits, species and gender being exactly what I wanted. That rarely happens, usually I sell all BOs I get, so its quite frustrating I can't assign them the ONE time it happened.
Off topic, I also agree that cross-career should have different station options. If a tactical officer has a cruiser, its still a tac and he should be able to switch the additional eng to a tac if he wants.