Why do the output colours differ from the input when using Filmic Blender in the VSE? As discussed in Colours from imported MP4 screencast video look dull in Blender, I recently stumbled across what I perceive to be an oddity with the new Filmic colour management: When working with imported 24bit images or video files (i.e. non-HDR) in the VSE and the colour management is set to Filmic, the colours in the output will not correspond to the input (see screenshots in question linked above).

This does not line up with how I thought Filmic works: My understanding so far was that (very simplified) it would scan the input for the maximum intensity and then scale everything down so that this maximum intensity becomes 1.0 (=pure white) - provided the input does contain intensities greater than 1. However, if I'm only working with 24bit input material, then this should never occur, shouldn't it? Or is Filmic not able to detect this limitation in the input material and always assumes a "buffer" on top of the 1.0 intensity?

To clarify: I already figured out how to get the desired output for the VSE (i.e. do not use Filmic). This question is exclusively about the Why of this solution.
Your understanding is incorrect. Filmic  blender does not scan the image to find high and low values. It does not normalize the image. There is a so-called "tutorial" out there that is spreading wrong information. 

Filmic blender works with with fixed parameters. Data within those parameters gets mapped to display referred values. Unless you feed images that are in scene referred values and within the range used by filmic blender, it makes no sense to use filmic blender's transforms for the VSE.

Even if you where to linearize display referred images, you would need to bring the scene referred values to the proper range to use of filmic blender's transforms. Most images imported into blender get linearized to display linear values (0 to 1). Filmic blender works on values much larger than 1, white would be around 16.9 in scene referred values.

Your images would need to be linear EXR files (with scene referred values in the range used by filmic blender) or they would need to be log encoded, to be linearized using the proper transform to fall within the range used by filmic blender. 

Please read the following link to learn more about filmic blender:

Render with a wider dynamic range in cycles to produce photorealistic looking images