bug#38452: 26.3; set-frame-position is slightly drifted

[Pascal Lambrechts <pascal.lambrechts@uclouvain.be>]

Hi,

I noticed a strange behaviour with the function set-frame-position.
This happens even when starting from `emacs -q --no-site-file`

If I evaluate  the following expression:

(let ((x (frame-parameter nil 'left))
      (y (frame-parameter nil 'top)))
  (set-frame-position nil x y))

( by  C-X C-E in the file or with M-: )

the behaviour that I expect would be  that the frame stays still since I use
the original left and top position to reset the position.
However the frame is slightly drifted by 10 pixel to the left and 8
pixels to the top.
If I repeat the evaluation of the expression the frame keeps moving.

More generally (set-frame-position ...) seems to be off by (-10,-8).

Best,
Pascal
  
-------
In GNU Emacs 26.3 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.22.30)
 of 2019-09-16 built on lcy01-amd64-030
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description:	Ubuntu 18.04.3 LTS

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-- 
Pascal Lambrechts  --  UCLouvain (SST/SC/MATH IRMP)
building: Marc De Hemptinne (Louvain-la-Neuve) - Local: B 430
phone: +32 (0)104x73161 
IRMP bte L7.01.02 // Chemin du Cyclotron 2 //  1348 Louvain-la-Neuve // Belgium