As the classic telerik controls are no more supported by telerik I try my luck here...
The problem occurs with a user control that dynamically creates a dialog
using some RadComboBox (version V2.8.8) controls. The problem occurs only when there are
items with umlaut (eg. 'Enhält') in the drop down box.
Is this issue known and is there a workaround for this? As for now we suggest to our customer to use another browser.
Here you find a working project demonstrating the issue with IE 11: http://www.filedropper.com/webcontrols-manualtests
There is also video and a word document showing the result in IE (not working) and firefox (working as expected).
Changing the code to use the latest telerik controls would be also an option, but I didn't manage to convert the code.
Hope someone can help!