Active apps get associated incorrectly

[Pierre]

System Data
***********
Linux distro: Elementary OS 5.0 (Juno)
window-manager: gala
Desktop-Environment: pantheon
Plank version: 0.11.4.33-fb62

Problem description
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Suppose you have a software "A", and you have a "A.desktop" file launcher. Suppose the launcher for "A" is locked on the plank.

The software "A" opens a document "/path/to_doc/foo" from the cli with

$ A /path/to_doc/foo

Suppose that I work with "A" on the file "/path/to_doc/foo" regularly, so that I build a custom launcher

[Desktop Entry]
Type=Application
Name=foo
Comment=This is the the comment
Exec=A /path/to_doc/foo
Icon=myicon
Terminal=false
Categories=Utility
StartupWMClass=foo

Then I am able to lock the "foo" launcher on the dock. Ehen click on the "foo " launcher it works, that is it opens the file "/path/to_doc/foo" within the "A" software. However the red light appears under the "A" dock launcher, and "foo" is associated to the "A" launcher on the dock.