wght/opsz axis mapping interference

[arialcrime]

When generating a variable font with mapped optical size axis I am experiencing some problems.

It looks and behaves alright in fontview 0.3.1, but eg. on Axispraxis (using Chrome) there is a visible jump whenever the slider is moved from the wght minimum with opsz placed anywhere not minimum. The axes’ defaults are defined at the minimum, but I also saw similar behavior when I put the defaults at the maximum. I attached a sample file to better illustrate the problem.

Is there any way I can prevent this?

WghtOpszTest.zip

[anthrotype]

I think it's related to the CoreText issue with avar reported by @arrowtype https://github.com/fonttools/fonttools/issues/1756#issuecomment-548807603

[arialcrime]

I can confirm that it works as expected in Chrome on Windows 8.1.