The problem is there also when the PAL speedup routine is active along with a 23.976 progressive clips with 2:3 pulldown flags. Now I don't check if pulldown flags are present.
In these cases, what about applying the IVTC option (Edit Title > AviSynth > Enhance) to remove the pulldown flags? The output would be a true 23.976 progressive clip, to which we can apply soft pulldown (23.976->25) or 4% speedup. Currently IVTC option is greyed out for everything but 29.97 interlaced, but you can easily tweak the frame rate and scan type clip properties within A2D. And if it works, I can activate IVTC by default for this scenario (input NTSC 23.976 progressive clips with 2:3 pulldown flags, output PAL).
Bye