r.thin creates triangle at acute intersection of two lines

[needelsd]

I have rasters that were generated using v.rast followed by r.buffer. Using r.thin on such a raster occasionally creates a triangle at an intersection instead of the expected two intersecting lines. All of the examples I have seen involve relatively acute angles (less than 25 degrees??).

This result is easily seen by using r.to.vect to create a vector, which then needs v.clean to remove dangles. I have attached a screenshot that shows the original (fat) raster in magenta, the vector with dangles in white, and the cleaned vector as (a thinner) green. There are numerous acute angles that generate the vectors I would expect, with one exception in the center.

[needelsd]

Vectors created using r.thin, r.to.vect, and v.clean

[hamish]

I think this is really a r.to.vect issue and not a r.thin one.

I am not sure if there is a correct solution though. i.e. this could be a (desired in some cases) feature, not a bug.

to remove the undangles maybe v.to.db upload line length then v.extract where line length > some threshold?

Hamish