Background horizontal mosaic isn't shown as expected when horizontal position is changed midframe

[GValiente]

Test rom:
mosaic-test.zip

mGBA tested versions:
0.8.1 and 6156-8d194fa.

If the horizontal position of the background is not changed midframe, horizontal mosaic is shown as expected.
Of all tested emulators, VBA is the only one which seems to get it right:

[GValiente]

Byuu seems to get it right too:

EDIT: Nope, the first column is wrong.

[endrift]

Do you have a non-animated version of this? It's kinda hard to compare against hardware when it's animating.

[GValiente]

mgba_1684.zip

VBA seems to show the correct output:

mGBA output:

[GValiente]

If it helps, here's the source code of the latest test rom:
https://github.com/GValiente/butano/tree/master/issues/mgba_1684