This is me correcting you... (you did ask) ;)
1) No, even if it's in seconds the marker still moves.I just tested it both ways:
Tempo = 120 BMP
Timebase = Bars and Seconds (both tested)
Marker on bar 3 (4 sec)
Tempo change (on bar 2, to 65 BPM)
Marker still on bar 3 (new time: 5.692sec)
2) Even if you were right, S1's default behavior would still be counter intuitive for film. I'm not about to compose music to a time grid that isn't musical. It would be impossible to work with. It also wouldn't get solved by temporarily switching timebases (assuming it were redesigned that way) because I'm not making tempo changes based on film hit points. That's what the markers are for in the first place. Tempo changes will either be musical decisions (like accelerando or ritardando)... which means markers need to stay locked to the film's frame regardless... or I might even change the tempo in order to find out what tempo will move the bar/beat to line up exactly with the film's frame. That one is a sync-to-film decision, not a musical one. But it's treated the same way. It's still how one would go about syncing hit points and keeping them synced in order to work, adjust, etc.
I apologize if that's not perfectly clear. But if you load a video, add markers, compose for that video, then make tempo changes... you'll find out that S1's current marker track behavior just won't work for film right now. At least, not for composers who ever use the tempo track. lol After working in software myself for years, I know most things aren't really bugs and it's often laughable when people say "this isn't just a feature for me". But if you try to score a film in S1, you'll find out very quickly that there's no way around this problem other than coding in a feature and it's about as universal as it gets for a user profile. Setting hit points and making timing adjustments as as normal as making noises with instruments in the film scoring world.
Hope that helps!