Unable to unset internal margins of a TBitBtn in Linux

[pierrealain6913]

Hello everybody,
I'm using TbitBtn's. The following problem appears only with Linux.
Version used : Lazarus : 2.2.6 ; FreePascal : 3.2.2
When assigning a bitmap to the glyph of the TBitBtn, there is a margin between the external edge of the button and drawing of the bitmap.
For example : with Windows : assigning a square bitmap of 28 to a button of 28 shows the bitmap in its entirety
With Linux (fedora 36 64 bits and Ubuntu 18 32 bits) I have to create a button of 38 to get the bitmap in its entirety.
Note : Acting on "BorderSpacing" parameters, "Margin" and "Spacing" does not change anything.

Anybody has a solution ?
Thank you for yous responses.