With one of the newest java snapshots, the mending has been updated with the prioritizing of the tool of lower durability as the "tool of need" for the xp orbs to mend.

Steps to Reproduce:

1. Get one tool and full armor with mending
2. damage the tool until its almost dead
3. Summon some xp orbs
4. hold the tool
5. Set your gamemode to survival and walk towards those orbs.

Observed Results:
You will see the xp bar being filled even tho the tool hasn't been repaird

Expected Results:
The tool should be repaird before the xp bar starts to fill

Screenshots/Videos attached: Not available footage