Insert artboard – wrong size when object has a stroke with Mitre Join.
Reproduced on two Macs with non-beta and on Windows with Affinity Designer in beta version.
How to reproduce:
Create an object eg. rectangle,
Set it's stroke width eg. 5pt,
Set Join: Mitre
Select that object
Use Artboard Tool -> Insert Artboard
Size of created artboard will be larger than it should be, there is no problem with Brevel and Round Join.
As you can see on a picture I attached, there are two rectangles, only difference is the first one has Round Join and the second Mitre Join.
Left artboard was created with proper size the second one has strange margin. Sometimes margin is bigger, sometimes smaller – I haven't figured out what it's size depends on.