A DESCRIPTION OF THE PROBLEM :
The ProgressBar control does not seem to support a horizontal/vertical property. So one way to get a vertical ProgressBar is by using the transformation APIs.
After rotating the ProgressBar 90 degrees its with and height properties remain the same as for the non-transformed control. This in turn impacts the width and height of its container pane. In my specific use case this is clearly an unwanted side effect as the container's size is used in some business logic.

I can see the same behavior in a different type of control, e.g. a Label.

I would be interested to know if this is a (known) bug or intentional behavior.