Downscaled shadow monitor window contains "background garbage"

[stdedos]

r27676

"Xpra-Python3-x86_64_4.1-r27676\xpra_cmd" shadow ssh://user@ip/0 --ssh="plink -ssh -agent" -d ssh --env=XPRA_SHADOW_REFRESH_DELAY=200 --title="@title@ on @@/@server-display@" --opengl=no --bandwidth-limit=6Mbps --desktop-scaling=0.75 --webcam=no --speaker=off --microphone=off --pulseaudio=no

args=--ssh="plink -ssh -agent" -d ssh --env=XPRA_SHADOW_REFRESH_DELAY=200 --title="@title@ on @@/@server-display@" --opengl=no --bandwidth-limit=6Mbps --desktop-scaling=0.75 --webcam=no --speaker=off --microphone=off --pulseaudio=no
XPRA_CUSTOM_TITLE_BAR=0
XPRA_EXECUTABLE=Xpra-Python3-x86_64_4.1-r27676
XPRA_NETWORK_ADAPTER_TYPE=wifi
XPRA_SCROLL_ENCODING=0

2020-10-16 11:56:31,540 parse_ssh_string(plink -ssh -agent)
2020-10-16 11:56:32,526 Xpra GTK3 client version 4.1-r27676 64-bit
2020-10-16 11:56:32,528  running on Microsoft Windows 10
2020-10-16 11:56:33,534 GStreamer version 1.18.0 for Python 3.8.6 64-bit
2020-10-16 11:56:33,869 created named pipe 'Xpra\11276'
2020-10-16 11:56:34,182 keyboard layout code 0x409
2020-10-16 11:56:34,183 identified as 'United States - English' : us
2020-10-16 11:56:34,368 Warning: libqrencode not found
2020-10-16 11:56:34,463  keyboard settings: layout=us
2020-10-16 11:56:34,466  desktop size is 4160x1440 with 1 screen:
2020-10-16 11:56:34,467   Default (1100x381 mm - DPI: 96x96) workarea: 4160x1400
2020-10-16 11:56:34,468     Generic PnP Monitor 1600x900 at 0x534 (309x174 mm - DPI: 131x131) workarea: 1600x860 at 0x534
2020-10-16 11:56:34,468     C32JG5x 2560x1440 at 1600x0 (697x392 mm - DPI: 93x93) workarea: 2560x1400 at 1600x0
2020-10-16 11:56:34,469  downscaled to 75%, virtual screen size: 5547x1920
2020-10-16 11:56:34,470   Default (1100x381 mm - DPI: 128x128) workarea: 5547x1867
2020-10-16 11:56:34,470     Generic PnP Monitor 2133x1200 at 0x712 (309x174 mm - DPI: 175x175) workarea: 2133x1147 at 0x712
2020-10-16 11:56:34,471     C32JG5x 3413x1920 at 2133x0 (697x392 mm - DPI: 124x124) workarea: 3413x1867 at 2133x0
2020-10-16 11:56:55,444 enabled remote logging
2020-10-16 11:56:55,451 Xpra GTK3 shadow server version 3.0.12-r27620 64-bit
2020-10-16 11:56:55,456  running on Linux Ubuntu 16.04 xenial
2020-10-16 11:56:55,459  remote desktop size is 6400x1440

(xpra_cmd:11276): Pango-WARNING **: 11:56:55.937: couldn't load font "Bitstream Vera Sans Not-Rotated 14.662109375", falling back to "Sans Not-Rotated 14.662109375", expect ugly output.
2020-10-16 11:56:56,969 UI thread is now blocked
2020-10-16 11:56:56,987 UI thread is running again, resuming
2020-10-16 11:57:16,752 server is not responding, drawing spinners over the windows
2020-10-16 11:57:17,342 server is OK again

[migration script]

this ticket has been moved to: ​https://github.com/Xpra-org/xpra/issues/2903