Yep, items always go first, that's why I wasn't exactly sure if this kind of bug can exist. But I'll try not to go too fast in the battles then! XD
Because it happened in the spring raid, I was trying to be realllllly quick in the battles. (Well heck, everyone does! XD)

I know this was awhile ago, but I wanted to add that mine was during the spring festival as well. I was trying to catch an easter pet. I will try to nab a screenshot if it happens again. I have gotten into the habit of opening a new tab and checking my stable each time it says I caught something now though, before I do anything else in the battle. Haven't had any other problems so far. @Ruinia,
It really seems like it was related to the event though, since yours was during the same

My captured pet is missing... It was the only opponent, I blocked instead of attacked so I know I didn't kill it, I saw the success message (I think), and the battle was over after that turn saying I won (but no xp so that's more proof I didn't accidentally kill it)...

Only reason it bothers me is cause I really wanted/needed it, and also I'm broke and can't afford any more traps...

Guess I'd better start checking BEFORE I click "explore" after a battle - It's too bad the log window doesn't store data for a few more turns, it would really help in situations like this

@Krazykat1980,

The combat log used to store everything, but it caused a lot of performance issues. Getting it to save only a certain amount of data given how it works is a lot harder than it would seem so unfortunately I haven't put forth the time for a more permanent solution.

As far as the pet, they can run away (in which you'd also receive no XP because you didn't defeat anything).

In the future, just make sure to check after using the Trap of what message you receive. If it says success (but no pet), then take a screenshot and I can investigate further.