GrCopyArea all 0s

Hi, I have an embedded Linux application that was previously using Microwin v0.91 (2005) and running on an old Arm CPU.
Now I'm porting the project to a new system (i.MX6 UL, armv7l) using the latest version of microwin.
My source code is well tested (>15 years of life) and was previously running without issues.

I have spent a few days adjusting the build config for this new system and the graphic library works as expected, APART from an issue that can be troublesome. We draw popups on our display and we need to backup the raster below the popup with GrCopyArea and restore it back after the popup gets deleted. Unfortunately, GrCopyArea seems not to work: it copies 0s to the raster when we try to restore the area below the popup, therefore after the popup is deleted we get a black spot below it.

I have debugged this and can't find anything wrong (from my little understanding of microwin guts). I reached one of the low level functions (rasteropGeneralLow) and can't see anything wrong (like a failed assert, a return before really copying the data, etc). The only thing I noticed is that the source and dest pitch are different: src pitch 8, dst pitch 16
What could be wrong?

The display is 1 bit only (the pixels can be on/off). These are some of the important fields in the config file:

SCREEN_PIXTYPE           = MWPF_PALETTE
SCREEN_DEPTH             = 1

SCREEN                   = FB

SCREEN_WIDTH             = 128
SCREEN_HEIGHT            = 64

MICROWIN                 = N
NANOX                    = Y
NUKLEARUI                = N
NX11                     = N
ENGINE                   = N
TINYWIDGETS              = N

LINK_APP_INTO_SERVER     = Y

HAVE_SHAREDMEM_SUPPORT   = Y

Start at the GrCopyArea call and follow it into rasteropGeneralLow, using the reported 1-bit framebuffer configuration and the source pitch 8 versus destination pitch 16 as reproduction details. Reproduce the popup backup and restore on the i.MX6 UL setup, then verify that the raster beneath the popup is restored instead of filled with zeroes.