Bug#986002: gimp: Cage transform creates visual glitches

[Pelle]

Package: gimp
Version: 2.10.22-3
Severity: normal

Dear Maintainer,

Cage transform creates visual glitches. These glitches appear just after
selecting the cage transform area, before any transformation are applied at
all. Sometimes these glitches appear in a totally different part of the image
than where the cage selection is at.

To reproduce:
  - Create a new 256x256 image
  - Put a bell pepper stamp in the upper left corner
  - Make a four point selection using the cage transform tool on the bell
pepper in the upper left corner
  - Now a large visual glitch (a heavily geometrically distorted bell pepper
but no distorted colours) may appear in the lower right corner
  - After pressing Enter to apply the cage transform, the visual glitch will
stay in the image, even if to points of the cage transform selection were moved
anywhere

-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable-debug
  APT policy: (500, 'unstable-debug'), (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.10.0-4-amd64 (SMP w/2 CPU threads)
Kernel taint flags: TAINT_CRAP
Locale: LANG=en_GB.UTF-8, LC_CTYPE=en_GB.UTF-8 (charmap=UTF-8),
LANGUAGE=en_US:en
Shell: /bin/sh linked to /usr/bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages gimp depends on:
ii  gimp-data            2.10.22-3
ii  graphviz             2.42.2-4+b2
ii  libaa1               1.4p5-48
ii  libbabl-0.1-0        1:0.1.86-1
ii  libbz2-1.0           1.0.8-4
ii  libc6                2.31-10
ii  libcairo2            1.16.0-5
ii  libfontconfig1       2.13.1-4.2
ii  libfreetype6         2.10.4+dfsg-1
ii  libgcc-s1            10.2.1-6
ii  libgdk-pixbuf-2.0-0  2.42.2+dfsg-1
ii  libgegl-0.4-0        1:0.4.28-3
ii  libgexiv2-2          0.12.1-1
ii  libgimp2.0           2.10.22-3
ii  libglib2.0-0         2.66.8-1
ii  libgs9               9.53.3~dfsg-7
ii  libgtk2.0-0          2.24.33-1
ii  libgudev-1.0-0       234-1
ii  libharfbuzz0b        2.7.4-1
ii  libheif1             1.11.0-1
ii  libilmbase25         2.5.4-1
ii  libjpeg62-turbo      1:2.0.6-4
ii  libjson-glib-1.0-0   1.6.2-1
ii  liblcms2-2           2.12~rc1-2
ii  liblzma5             5.2.5-2
ii  libmng1              1.0.10+dfsg-3.1+b5
ii  libmypaint-1.5-1     1.6.0-2
ii  libopenexr25         2.5.4-1
ii  libopenjp2-7         2.4.0-3
ii  libpango-1.0-0       1.46.2-3
ii  libpangocairo-1.0-0  1.46.2-3
ii  libpangoft2-1.0-0    1.46.2-3
ii  libpng16-16          1.6.37-3
ii  libpoppler-glib8     20.09.0-3.1
ii  librsvg2-2           2.50.3+dfsg-1
ii  libstdc++6           10.2.1-6
ii  libtiff5             4.2.0-1
ii  libwebp6             0.6.1-2+b1
ii  libwebpdemux2        0.6.1-2+b1
ii  libwebpmux3          0.6.1-2+b1
ii  libwmf0.2-7          0.2.8.4-17
ii  libx11-6             2:1.7.0-2
ii  libxcursor1          1:1.2.0-2
ii  libxext6             2:1.3.3-1.1
ii  libxfixes3           1:5.0.3-2
ii  libxmu6              2:1.1.2-2+b3
ii  libxpm4              1:3.5.12-1
ii  xdg-utils            1.1.3-4
ii  zlib1g               1:1.2.11.dfsg-2

Versions of packages gimp recommends:
ii  ghostscript  9.53.3~dfsg-7

Versions of packages gimp suggests:
pn  gimp-data-extras          <none>
pn  gimp-help-en | gimp-help  <none>
ii  gvfs-backends             1.46.2-1
ii  libasound2                1.2.4-1.1