The pen tool and shape tool both have a strange quirk where you cannot draw a shape over top of another shape another layer or even a guide. It doesn't matter if the layer underneath is locked, it simply won't let you draw anything. Instead it moves the object below. There is another post about locked layers where this issue was mentioned. I don't really understand this. I'm forced to use the free selection tool and then covert selection to shape to create compositions.
The simplest solution would be to have a key command such as 'control' which would switch to drawing a new shape no matter what's below whether that's a guide or layer. This would be similar to moving a layer and holding 'command' to ignore guides.
A nicer solution (nicer because it wouldn't require people to know a key combo) would be to remove the dual nature of pen tool also being an arrange tool and make the pen tool only draw new shapes, thereby getting rid of this problem. Instead, the shape properties could be under 'arrange' and under 'style' sidebars. I get the idea of having the options that go along with a shape being under the same sidebar as the tool that actually creates them but it's more cumbersome than having tools separated from an inspector with the shape's traits. Sketch does it this way and is quite a bit easier and actually feels simpler.
What features would you like to see in Pixelmator Pro?
Great to hear! Looking forward to it