Lottie matte rendering artifacts with lines

[andrewvarga]

if I have a rectangle and apply another one to it as a matter layer it works.
However if I have a line (2 point bezier path) with a large stroke, which also looks like a rectangle and apply a matte to that, I get some strange artifacts in the lottie web player, the bodymovin player or in lottiefiles Playground.

This is what it should look like (the bottom shape is a line, both are masked by a rectangle):

This is what it actually looks like (ignore the transparent background, note the weird shape of the bottom shape):

To me this looks like a bug in the Lottie player / renderer. Can someone confirm and advise about a fix or workaround?
Thank you!

Here is the lottie file in ques
matte_bugs.lottie.json
tion: