Anchor doesn't seem to work properly with round rectangles

I would expect the following code to draw 3 rectangles beneath each other with their `right` corner aligned on `X`.
```
roundRect(300.0, 90.0, 0.0) {
anchorX = 1.0
xy(300.0, 100.0)
}
roundRect(200.0, 90.0, 0.0) {
anchorX = 1.0
xy(300.0, 200.0)
}
roundRect(100.0, 90.0, 0.0) {
anchorX = 1.0
xy(300.0, 300.0)
}
```
However, it will instead show three rectangles, mostly aligned to right, with +-20 pixel variance.

Reproduce the issue in Korge using the three roundRect calls from the report and inspect the anchor and positioning behavior for round rectangles. Compare the rendered right edges at X=300; done means all three rectangles have their right corners aligned without the reported pixel variance.

Written by the indexing model from the issue text.