I can sound rude but I'm not sure what's the point.
You were getting to l25, so apparently you were just hitting a peak of the XP possible to gain, rendering all further gain gone. You don't get a notification how much XP do you lose by that act of "overkill".
To avoid that, one can either use two carry pets (if it's safe) or leave that pet to a less-rewarding encounter (wilderness for example). On the other hand, if your pet is 19+ and the XP bar shows first 20% of its level, I'd recommend using upgrading stones instead. Nothing disallows to get that situation on purpose once you know by heart how it works in details.
There's also this whole deal with a square function describing the way pets gather experience, so you may want to check the content of @Jerebear's signature.
On Crysa specifically… well, Sandstorm
I wait for a first post or comment saying directly "bring back MoP" in the context of pet content.
Unless there's already one, I'd like to see it.