FrameFlex Inconsistancy

I have found some inconsistancy with linking media and FrameFlex in Source Setting.

720P-Project (format 720P50)

1. I link to 720p50 media.
2. I open Source Setting, FrameFlex. Raster Dimension is shown as 1280x720 (correct). Image Size is shown as 1920x1080. Why not 1280x720?.
3. I transcode the linked clip and get a 1280x720 clip, independant of applying FrameFlex or not (marking box in the tarnscode window).
4. I can place the transcoded clip on a 1280p50 timeline, and have no FramFlex "S" on it (as expected).
5. I place the same clip on a 1080p50 timeline, and also have no FrameFlex "S" on it. Video fills the whole screen format of 1920x1080.
6. I place the same clip on a 3840x2160 timeline, and the FrameFlex "S" is shown. Why here and not on a 1080P-timeline?

1080P-Project (format 1080p50) 

1. I link to 720p50 media.
2. I open Source Setting, FrameFlex. Raster Dimension is shown as 1280x720 (correct). Image Size is shown as 1920x1080.
3. I link to 1080p media.
4. I open Source Setting, FrameFlex. Raster Dimension is shown as 1920x1080 (correct). Image Size is shown as 1920x1080.
5. I place both clips on a 720p50-timeline. Both clips have no FrameFlex "S" indicated.
6. I place both clips on a 1080p50-timeline. Both clips have no FrameFlex "S" indicated.
7. I place both clips on a 3840p50-timeline. Both clips have FrameFlex "S" indicated.

UHD50P-Project (format 2160p50)

1. I link to UHD-media.
2. I open Source Setting, FrameFlex. Raster Dimension is shown as 3840x2160 (correct). Image Size is shown as 3840x2160 (also correct).
3. I switch the project to 1080p50.
4. I link to UHD media.
5. I open Source Setting, FrameFlex. Raster Dimension is shown as 3840x2160 (correct). Image Size is still shown as 3840x2160, and not 1920x1080.
6. I transcode the clip without checkmarking the "FramFlex" box in the transcode window. I get a transcoded clip in 1920x1080 format encoded with DNxHD 240.
7. In Sorce Settings FrameFlex, I change Image Size to 1920x1080.
8. I transcode the clip with checkmarking the "FramFlex" box in the transcode window. I get a transcoded clip in 1920x1080 format encoded with DNxHD 240. 
9. I place both transcoded clips on a 1080p-timeline. The clip created in step 6 has a FramFlex"S" on it, while the one from step step 8 has not.
10. I switch the project to UHD50p (format 3840x2160). The FrameFlex"S" on the two clips have changed their locations. Now the clip from step 6 has no FrameFlex"S) while the clip from step 8 has. This behavior is not understandable.

Can an Expert from Avid explain this?

Joachim

P.S.

If I make a color correction on the clip with FramFlex"S" shown, MC crashes. If I make a color correction on the clip with no FrameFlex"S" shown, MC does not crash.