Mask & 9-Slice Scale Issue

I have a MC with image in it
and a MC mask > vector box with rounded corners
The MC mask also has 9-Slice Scale (set as appropriate for the rounded corners)
When I test without mc.setMask(“mc_mask”) it works fine…
…as soon as I set it as mask, the 9-Slice is no longer working and my rounded corners look ugly
I don’t want to manually do the whole thing just for some rounded corners

Any help will be appreciated