[USER] Thanks for looking! You actually successfully replicated the oddity! Please take a second at your video. :)
In the top button the splash is misaligned towards the bottom of the trapezoid. 
And if you try once again with the changes I made in the linked PR above you can see that it is fixed. 
At least for this particular scenario and likely for all since the inkwell now used the exact same shape as the parent material. 
[USER] Any reason the InkWell shape parameter wasn't also resolvedShape!.copyWith(side: resolvedSide); in your merge?
And if we are really looking at it. 
You can see that despite using the same outlineshape the shapes differ. 
And in fact, the splash of the first shape is the shape of the second trapezoid.