Bottom of side-tiled windows are cut off when modal dialogs are opened.

[jroyvde]

Reporter Info

• Materia version: 20200320
• GTK3 version: 3.24.23
• Distribution (and version): Fedora 32
• Desktop environment (and version): GNOME 3.36
• Related application (and version): Seemingly any GTK application featuring modal dialogs

Actual Issue

Upon opening a 'modal dialog' (such as those featured in many default GNOME apps), if the window the dialog is opened from has been tiled to the left or right (by dragging or using GNOME's keyboard shortcuts), a number of rows of pixels on the bottom of the base window will seem to disappear (on my 1920x1080 display, 18 rows of pixels are cut off). This occurs on all regular, light, dark and compact variations of Materia. The problem only occurs if 'Attach Modal Dialogs' is enabled in GNOME Tweaks (which is the default behaviour in GNOME on Fedora). Disabling this option seems to mysteriously solve the problem.

Steps to Reproduce

1. Ensure GTK theme is set to Materia and 'Attach Modal Dialogs' is enabled in GNOME Tweaks
2. Tile a window to the left or right by dragging it or pressing Super+Left/Right
3. Open a modal dialog from that window (e.g. the 'About' menu in GNOME Files)

I've tested with the Adwaita theme as well as Plata and can't reproduce the issue with either.