I see what you mean, but I didn't do anything special for PAL mode. The different "shimmering" effect is a result of the "burst phase" parameter of nes_ntsc_blit() getting different values when PAL mode is enabled.
You can see the code at
https://github.com/fo-fo/nintendulatord ... X.cpp#L752Because PPU::DidShortenPrerenderScanline is never TRUE for PAL, burstPhase is increased by 1 on every frame (modulo 3). In NTSC mode the increase is 1 or 2 depending on whether the frame had a "missing dot" on the prerender scanline.
I think Nintendulator may actually have a bug in that it has the "missing dot" behavior happening in Hybrid (Dendy) mode. If this bug is fixed, then the NTSC filter should look same as in PAL mode. I will probably fix the bug in the next version.
Yeah I can't say for sure whether the "missing dot" behavior is happening on Dendy. This page
http://wiki.nesdev.com/w/index.php/Clock_rate says it shouldn't (in "Total number of dots per frame"), but I'm not aware of any test ROM or research that tests this behavior.