Opensubdiv does not know topology of uv map, only mesh. So corners created by placing seams on continous mesh are not seen as corners by opensubdiv.

I will look into it.
When you add another modifier after subd, that does nothing (eg. bevel with limit set to weight) it fixes it also.
Probably Blender takes normals calculated by OpenSubdiv which are very good when using limit surface (that's one of the points of using it in the first place) but are not that great when limit surface is disabled.
I assume enabling autosmooth (or adding mod after) overrides normals with ones calculated by Blender.

Thank you.

So this workaround is almost 2 years old, do we know, if it was fixed on OSD side? I can say, that I don't observe crash with this change.

Needs to be rechecked https://developer.blender.org/rB443e42d may be fixing this.

• merge master
• 'Boundary Interpolation' -> 'Boundary Smoothing', 'Edges Only' -> 'Corners Only', 'Edges and Corners' -> 'None'

• variable naming
• UI description

• merge master
• disable, instead of hide, quality settings in non-adaptive mode
• change description of the toggle as per request

Yup. Brecht's comments were only about naming and missing description.
Those are fixed now.

Rebase on master

Rebase on master

• use_limit_surface, negative property
• move option to adv. panel

Reasoning behind putting this option near the top was that it has significant influence on modifier output similar to "Simple" and "Catmul-Clark"

UI labels correction

• Add versioning
• Move converter to common place
• Comment formatting.

@Sergey Sharybin (sergey) function subdiv_vtx_boundary_interpolation_get is duplicated, please advise, where to put it so both modifiers can use it.

• invert flag
• change naming
• move comment

• Remove boundary interpolation option
• Change user facing labels.
• Add code comments about UV fix.
• Change title and description to reflect more limited scope of patch.

Fix UV mangling in non-adaptive mode.

In D8413#205363, @Sergey Sharybin (sergey) wrote:

It is not acceptable to have UVs knowingly broken in any modifier.

Move conversion function as requested

• There is a bug in OpenSubdiv's face-varying evaluator. This makes it so UVs are all messed up once you go uniform subdivisions. Surely, this is to be reported and fixed in OpenSubdiv, but because of other points it was not a priority so far.