Color Page - Matte size not matching

I am having a really hard time here. The size of the external matte is not matching my footage size.
What I did
- imported simple JPG img sequence (100 frames FullHD, square pixels) no alpha channel
- imported b/w PNG img sequence (exact same specs as above, rendered in same CG app/project/rendering)
- dropped the JPGs on timeline, opened color page, dropped PNGs on color page (recognized as external Matte )
- connected matte, and tweaked say offset -> the affected area is obviously double the size of the JPGs/PNGs
- reset all node grade, reimported footage(s), reopened DR, uninstalled, cleaned UserFolder, reinstalled DR...

No change! I am pulling my hair out! Yesterday when I shut down the computer everything seemed fine.

This shows the (ridiculously simple) setup and how the pictures dont match with the result...

Screenshot 2021-05-13 190305.png (405.38 KiB) Viewed 476 times

Any help appreciated...

Cheers
Roger

Can anyone tell me what these icons mean? Seem to be a "external matte used". But when I un-connect the external mask (or delete it, even delete it from the project) the icon wont change or disappear...

Screenshot 2021-05-13 191358.png (28.12 KiB) Viewed 477 times

Another problem I have at the moment brought me to test with internal scaling bugs in resolve. It seems as if DR has some severe bugs when scaling images (that is viewer content) in certain situations regarding mattes and/or qualifiers.

When setting my timeline playback to full res (had it at half res) suddenly the external masks seemed to be normal sized again in color page.

This is really a show stopper. Took me half a day to figure out (still praying it is really solved)...

So I tried to find a workaround and things are even more weird. I disconnected the matte just for tweaking colors (which only makes so much sense, since you have to ignore the false colors of the areas that are masked for exactly that reason). Well - when plugging back the connection the matte was non-inverted (inverted it manually before). So I had a look at the nodes matte section but the "invert" button still was active. Fiddling with it I remarked that the button´s status does not update reliably. So when disconnecting and re-connecting a external matte you could (or could not) get an double-inverted result. And the GUI icon for inverting the matte could (or could not) show the invertion...

To workaround the workarounds problem I tried to just hit CTRL-D (disable node) on the external matte. Resolve instantly crashed. This is just the case when beeing in split screen mode...

No one having experienced this? I had a shot matching to do and it was a desaster. I had to take screenshots and overlay them over resolve (with this nice little freeware PureRef).