Interpolation break in terminals

[luxpio (Lucas Portron)]

Hi everyone,

I’m running into an issue with terminals breaking during interpolation in Glyphs, and I was wondering if anyone has experienced something similar.

In my masters, the terminals look clean and consistent, but as soon as I interpolate, some terminals start to deform or fall apart.

I’ve already checked:
contour compatibility between masters
point order and number
path direction
drawing extremes

Is this a known behavior in Glyphs?
Thanks in advance for any insights!

[GeorgSeifert]

That looks like a kink. It is explained here: Multiple Masters, part 2: keeping your outlines compatible | Glyphs

[SCarewe (Sebastian Carewe)]

Have a look at this thread:

Variable straight slanted shape bug

For the relative angle of two lines not to change in interpolation, either the angle must stay the same, or the ratio of both line lengths must stay the same. It is better known when curves produce a kink in interpolation, as shown in “Designing Multiple Master Typefaces” (Adobe 1995, 1997), but is also true for lines. [Bildschirmfoto 2022-10-15 um 17.54.48] The problem is that not only the slant of the letters changes, but also the top bar of the T gets fatter.