Hello,
The tooltip of XP Shard says consumption while sneaking the entire stack at once.
But it does not.

That should work. It seems I've not added any code to implement it for 1.12 :(
I'll get that fixed up for the next release.

Just for my reference - this was in 1.10, but somehow the code has vanished for all other release.
599dd49
Port the code over into 1.12.

Fixed - thanks for reporting that.

I just noticed this myself. At least it's fixed. It's a bit annoying when you've accidentally left a factory running for a few hours and got around 60,000 XP Shards and want to turn them into Fluid XP.