gTile@shuairan: Windows using CSD/GTK HeaderBar are positioned with an offset

[sphh]

 * Extension version/Build date: Version 1.0.0 (2020-10-12 13:35:19)
 * Cinnamon version: Cinnamon 4.8.5
 * Distribution: Mint 20.1

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@veryangryman ?
@jaszhix ?

Issue
If the window to be positioned used the CSD/GTK HeaderBar, it is offset to the right and bottom. Here are some screenshots with Gnome Terminal and Tilix (but exactly the same behaviour can be seen with other programs using CSD/GTK HeaderBar). All terminal windows are moved to the top right corner with the help of gTile:

Gnome Terminal

Tilix with CSD enabled (under the Tilix Window, the previously positioned Gnome Terminal can be spotted)

Tilix with CSD disabled (it fully covers the Gnome Terminal)

Steps to reproduce

1. Start Gnome Terminal and move it to a fixed position with the help of gTile.
2. Start Tilix and move it to the same position with the help of gTile.
3. Change the preferences of Tilix to not use CSD, restart Tilix and move it to the same position with the help of gTile.

You could also use another program using CSD/GTK HeaderBar.

Expected behaviour
All three terminal windows should end at exactly the same position.

Other information
This might easily be a bug in the realm of CSD/GTK HeaderBar …

[d-sko]

Similar bug with Chrome, but it is shifted a little to low and to far right: