Yeh my cats have also done this.
I partnered a cat. It gave birth...then the father bred again within 30 secs afterwards with another nearby cat who was at 100% love. It appeared he lost his love on the first breed however he still bred a second time with the other cat.
It was not a sim rollback because I was standing beside it when it happened. (Callie Cline also witnessed this and told me to make a support ticket which at the time I didnt...my bad...but I was about to leave for a 2 week holiday
) Plus a sim rollback would mean the first box would disappear.
Proof:
http://gyazo.com/f3d0a4a53a630c5e2128a138a9f619b1
Its the two cats born on the date of 13-10-18.
IDs: e7086af2-b1dc-bdc3-e4be-84146fbd5c7e
b0044ca3-dea0-5243-6180-48bcaf6eee3a