Strange situation regarding squad registration. Can't play players but assistant can?

Just a little background info... I'm playing a lower league save trying to jump up the English leagues. Gone from League 2 to League 1 to Championship in progressive seasons so naturally my squad is a little random. There are still some stragglers who could barely make League 2 level yet I'm desperately in need of Championship quality players if my recent form is anything to go by! So I get to around Oct/Nov in my Championship season sitting 1 place from bottom and decide my team desperately needs some better players. Unfortunately I committed a pretty stupid error and have signed too many players. I thought I'd be able to offload some but literally NOBODY wants any of my crappier players and I have currently registered a full squad of 25.

So basically I have 3 or 4 players much better than the rest of my squad that I'm unable to play. Their names have no message next to them but obviously they're not registered. I'm not an expert on how squad registration works but I'm guessing I need to either wait until the next window in December to unregister some crappy players and register my new ones OR could I try and release ones I've already registered?

Anyway, I was pushed for time for one game in early December and I decided to let my assistant manager play the game while I holidayed through the match. Much to my surprise he managed to play all 4 of my new signings despite the fact they weren't registered? Needless to say, we won the game! We had another game a week later which I again controlled myself and yet... I can't play these players again?

What gives? Is it a bug? Or perhaps I just don't understand squad registration fully? I'm all ears!

It's a bug that your assistant manager is able to play them. I think SI know about it as it's been mentioned before. Still create a thread in the bugs forum though. You have registered hthe 25 players, so are indeed correct and won't be able to register your new players until January. If you only had 24 registered, you could still register 1 player.