This issue occurs with all farm mobs (cows, pigs, sheep and chickens). When feeding a mob, in goes into love mode. While in love mode, you can continuously feed the same mob. If it doesn't breed and love mode stops, you can immediately feed it again to start love mode.

This causes a big issue with breeders that use water to bounce the mobs up and down while you feed them. This also can cause you to feed all your stacked item (hay, seeds, etc.) to a single mob.

Once you feed two mobs of the same type, they will breed and afterwards, you can no longer feed them until after the cooldown period, which is working as intended.

The way it should work is you cannot feed a mob if it's already in love mode. And if it did not breed and fell out of love mode, you should not be able to feed it again until after the cooldown time has expired.

To reproduce (It's best noticeable in survival mode, but can be done in creative):

1. Find a farm animal and feed it.
2. While it is in love mode, continue to feed it. You'll notice that you're going through your stack of feed.
3. Wait until the love mode has stopped and feed it again. The mob will enter love mode again. Normally, you shouldn't be able to feed it again until after the allotted cooldown time (5 minutes or something like that).