Why

[Heather]

They were on 9 frames and the super under was complete for winter feed. Their behaviour was poor (being polite) so I am thinking queen failure. But all gone , so hope they bulked up other colonies.

 

[Hebeegeebee]

If their behaviour was poor, then it's a problem you won't have to deal with next spring.

 

[Heather]

Absolutely.. but I am always reluctant to cull.. sorted that one for him.

 

[Curly green finger's]

The OP said it was a good sized colony. I use single brood nationals and always leave a super on over winter.

Same here really, not all colonys have supers left on only the biggest.
No issues for me.