Extend surface error

Extending this surface, both internally and externally (with funds=no) gives a problematic result.
extend surface problem.3dm (185.1 KB)

is these the errors you re talking about ?

originally only was build for untrimmed surfaces. (until Rhino 5 or 6 ?)
so extending trimmed surfaces maybe is a compromise.
and your single-curve / sharp corner trimming is maybe a bit to sophisticated special case for this command ?

what s the workflow to repeat the error you re talking about ?
what is the result you re expecting ?

you’re surface is planar - so why don t you work on the trim curve, use _offset and _planarSrf ?

kind regards - tom

Don’t properly call it a “mistake”. I understand that planar form has a singularity. I would have expected the command to work. it is normal to use other roads, the ones you indicated. Almost at version 8, could a user expect something more, or is it a sacrilege?