Indeed I verified that the described issue exists in the current version of our controls when the culture is set to pt-BR. I forwarded the issue to our developers and they will start working on its resolution. At a meantime you could try using the following workaround:
Handle the OnValueChanging
and replace the "de" separator with "/":
newValue = eventArgs.get_newValue().replace(
" de "
Additionally I am sending you a simple example, please check it out and let me know if it helps you.
the Telerik team
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