A common UI paradigm is the „LIFO“-paradigm (here in this variant: „Last called, display on top“).
The rendering‘s z-ordering should be accordingly.
I assume a problem with incorrect z-order on overlapping dialogs/windows (first called dialogue is on top).
To be reproduced by:
1.) Open medium stand‘s status dialogue by left-clicking it.
2.) Press <TAB> button (or any menu dialogs or „Airport Status“ button)
=> Please see attached screenshot with additional information
=> See ACEO-4175‘s („b.zip“ + „output_log.txt“) // but probably not savegame specific!