Hi Martin,

> There seems to be something odd happening when I edit the size of an arc
> if it lies directly on top of a circle.

There's a feature in the resizer where if you're resizing a line or an arc, it scans through all the other objects to see if there are other existing curves that touch the current one at an endpoint, and if they do it uses that endpoint as the scale origin.

That enables behavior like this - when you edit this radius of this arc here:




The edited arc gets scaled like this so that it's still connected to the adjacent line:




The same thing is kicking in for your case with a circle - a circle also has a start and end point to it even though you don't normally see it, and if the arc being sized touches that point at one of its ends it will get anchored to it.

I'll tune this mechanism up so that it will skip closed curves when it's looking for any other touching curves since it's pretty weird behavior in that case.

Thanks for reporting the problem,

- Michael