Corrupted Skill gem levelling bug with Sunder in Ancestral Warrior totem

I hope this is not a duplicate entry. Here is what I got:

- I have a level 19 Sunder corrupted to level 19+1 equipped in a level 20 Ancestral warrior totem
- I get a level 20 uncut skill gem
- I cut the skill gem and select the Sunder 19-->20 option as to my knowledge corrupted gems can still be cut to higher levels, hence it is also offered like this in the cut skill gem window

Result:
- to my surprise, the Sunder in the ancestral warrior totem is still level 19+1 and instead, I have a new sunder gem equipped which is the level 20
- of course, I would have expected that my sunder in the totem gets upgraded to level 20+1