Custom time signatures and multimeasure rests

Create a score (a single line will do).
Leave a few rest bars, then add some notes.
Use time signature properties to change timesig to a special character.
Press M to create flip to multirests - special character disappears.
(you may need to press M twice more)
Press M again - the special character reappears so long as there is not a multirest following it.
(See also png file)
This has been bugging me in MS3 ... now it's n MS4. Oh dear!