Hi Brian, yup that's definitely a bug. It looks like it has to do with a new caching mechanism in v4. I'll see about fixing it, thanks for reporting it!

re:
> (Also I see that Blend does not work between the ends of one open curve, in either MoI3 or MoI4beta.)

Yes, you'll have to split a single curve into 2 pieces to do that particular blend.

- Michael