The observed change has been introduced after the last official Service pack (R1 SP1 2017.1.223) and it could be observed in our latest internal builds. At this point adding HTML to Kendo UI window's title property
is no longer supported. This change has been introduced in order to prevent any possibility of a script injection when using html in the widget title.
If this is important feature that you want to have, you can visit our Feedback portal
and create a new feature request for Window title template.
As a workaround I can suggest you using jQuery API to prepend/append the needed html:
"<span class='custom'>drag me</div>"
If you have any other questions, please do not hesitate to contact us.
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