Before:
After:
File:
extend-flips-blend.3dm (154.8 KB)
Try _HistoryPurge
I think you’re missing the point.
History should just work.
In fact, I can’t think of a simpler example where it should just work…
2 Likes
Got it… Something must be wrong.
PS: maybe change your title to “Extend surface breaks blend with history”…
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I believe this is fixed in the WIP. I will check.
-Pascal
Nope, I just confirmed… it’s very much not fixed.
I have 7 blends in a fairly simple design that I’m trying to do rapid design iteration on… and it is not very rapid at all… and yes, it affects ALL of them! Repeatedly! Even if you re-do one, and then extend again, the same thing happens! 
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This is adjacent, not sure if it deserves its own thread or not but before trim:
And after trim:
No reason for any of the unaffected edge IDs to change (and just to pre-empt the inevitable technical answer: Yes, I know a trim curve goes all around even untrimmed edges in Rhino but as an end user I simply don’t care… that’s a technical debt McNeel engineers have to clean up).
mutual-trim-blend.3dm (170.1 KB)
I’ve also noticed this: