Hello Mike Oliver,
Indeed you are correct about this change. It was introduced with the official Q2 2012 release (2012.2.607). The behavior have changed as a result of fix for the MaxLength property. The problem is that in the different browsers, the new line character is interpreted differently by the JS engine. For example in IE8 it is count as 2 symbols, while in IE9 it is 1 symbol. Our developers tried to fix that in the RadTextBox client side scripts, but it looks like they have missed this scenario.
Anyway I have a logged a bug for this behavior and notified our developers for it. Unfortunately I can not provide you with exact estimate about when it will be fixed. We will give our best to include in the Q3 2012 release expected in the mid October. Meanwhile you can follow the status of the issue
in our public issue tracking system.
I hope this helps.
the Telerik team
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