Elemental Overload (Possibly a bug)

Hi fellow shaman,
I recently noticed that when a lava surge procs in the mid of casting a lightning bolt and you throw both spells out at the same time, it's ALWAYS only 1 of the two spells trigger mastery, I mean I have 55% mastery, chance of them both triggering mastery should be decent, but I've never seen that happen.

so the only explanation would be Elemental Overload is bugged, if it is indeed a bug, it hurts elemental shaman dps A LOT because of how frequent lava surge can proc during lightning bolt casts, and every time it happens, you'd lose a LB , or worse a LvB overload dmg.

though I still can't be 100% sure, because I've not played retail mop, so correct me if I'm wrong.

Edit:
This is confirmed a bug, if you are reading this please up vote it in bug tracker
https://www.warmane.com/bugtracker/report/8543

How to test:
1. reforge everything to mastery
2. wait for a lava surge proc
3. start casting a lightning bolt and spam your lava burst button
4. observe if you ever get a lightning bolt overload AND a lava burst overload

I have already tested this myself multiple times with 65% mastery, only scenarios 1,2 and 3 happen when firing a lava surge proc at the end of a lightning bolt cast:
1. lava burst + lightning bolt
2. lava burst + lava burst overload + lightning bolt
3. lava burst + lightning bolt + lightning bolt overload

This never happens:
4. lava burst + lava burst overload + lightning bolt + lightning bolt overload

tyvm for post and doing bug report cbbffljz

Im curious if echo of the elements is also affected by this bug.