Different behaviours of Remove Overlap

Glyphs
1

Hi, I’m looking for clarification on Remove Overlap.

While checking OTFs with checkOutlinesUFO, I realised that I’m getting different results in these cases :

  1. Check Remove Overlap on export
  2. Add the RemoveOverlap filter to the instances (seems the same as the option above)
  3. Add the RemoveOverlap filter to the instances AND check Remove Overlap on export

Basically, the outlines are cleaner with the double check. Only then will it remove collinear lines (see this Topic).

Does the algorithm run twice and simplify the outlines? In this case, could it simplify them too much?

Thanks