And that's because collision vertex DO have decimals and they're not shown at all in the UI, so can we please have whether a decimal display, or snapping to round numbers?
If you look closely, you can see that the lines at not exactly flat, but it's hard to see really, and I doubt it would be perfectly flat anyway
Here is a capx to illustrate that.
The green and yellow boxes are placed exactly the same way
Green boxes have a "perfect" collision polygon, with the automatic detection
Yellow boxes have the same collision vertex coordinates, as far as the UI can tell, but in fact there are decimals, as I placed them with the mouse
Green boxes will stand and yellow boxes will fall
For now I guess I will always move the vertex with the keyboard arrows, but whether a snap or real decimals are necessary here I believe