After many years annoyed by this issue, decided to make a simple 3ds Max script and it works. Those still animating with Biped like me, know that every time you set a new key, if needed you have to set manually the continuity, 3ds Max doesn’t remeber the last value or allows you to modify the default, always 25. Going there dragging the spinner or typing 0 is slow if you have to do it many times.
This tiny macro script does the job, copy and save, or just run the code:
macroScript BipContinuityZero category:"pX Tools" ( idx = getkeyindex $.controller sliderTime if idx!=0 then ( bipkey = biped.getkey $.controller idx bipkey.continuity = 0 ) )
What I did was assign Ctrl+0 keyboard ShortCut to BipContinuityZero macro, remember you’ll find it in “pX Tools” category.
Select the Biped node, position the timeline bar over the key then press Ctrl+0. Done!