Thank you for writing.
I have tested the described case and I can confirm that it is an issue with our designer. The issue is logged here: http://feedback.telerik.com/Project/154/Feedback/Details/128476
. Feel free to add your vote/comment to it.
I have updated your Telerik Points
for this report.
Meanwhile, you can create the desired RoundRectShapes and apply them at runtime.
Check out Telerik Analytics, the service which allows developers to discover app usage patterns, analyze user data, log exceptions, solve problems and profile application performance at run time. Watch the videos
and start improving your app based on facts, not hunches.