Bug details: OS: Windows 10. VS: 2015 professional Telerik version: 2015.2 SP1 Code sample: <Window x:Class="RadMaskedInputBug.MainWindow" xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation" Title="MainWindow"> <Grid> <telerik:RadTextTimeInput /> </Grid> </Window> The designer crashes and shows only the exception: InvalidOperationException: Can only base on a Style with target type that is base type 'RadMaskedTextInput'. UPDATE: Telerik has submitted a bug report to Microsoft. You can check its progress here: https://connect.microsoft.com/VisualStudio/feedback/details/2005303/designer-error-can-only-base-on-a-style-with-target-type-that-is-base-type-customcontrol-when-a-style-is-basedon-a-style-of-an-abstract-class On 21/12/2015 Microsoft commented that a fix has been submitted and will be available in the next update.