The HotStart Challenger is most complex aircraft simulation ever coded on any plateform so far by far (I still can't understand why so many people don't realize this), so rest assured these behaviors are very close to the real thing. Anyway, the first thing to understand is that the Challenger is no Boeing or Airbus. So you should not except similar behaviors everytime.
The way the ATS works in the sim is the way the real thing works. Same thing for VNAV wich isn't VNAV as most Airbus/Boeing pilots/simmers understand it : It's a modifier.
You should join the Hotstart Discord Channel. You'll find many many answers there.