When you have set the Windows task bar to auto-hide and you maximize an RadRibbonWindow, you are not allowed to visualize the task bar on top of the RadRibbonWindow. Available in LIB version: 2015.1.2303
Yeah, this is really a very annoying issue for our clients as well! Please fix this as soon as possible. It is known for more than 2 years now!!
This is an important issue for our clients.