The cause is in the QuestLog Info window (the one drawing the quest description and informations).
To add the two buttons for Tracking and Log I turned it in a "Horizontal Command Window"
It's a trick I did to save time on the button generation and to be able to use the built in navigation of RMMZ
While it works ok without MessageActions, this plugin add a fix to calculate the button text and it works flawlessly in a "normal" horizontal command window but in a "special" window like QuestLog it generates negative X values for the text
All I need to do is to assign a ProcessText function that recalls Window Base instead of Horizontal Commands Window and block the alignment fix of MessageActions only for the QuestLog Info window commands