This problem only happens when the RichTextBox is hosted inside a RadWindow. It is fine when it is embedded in a normal page.
If you have browser zoom (bottom right for IE 8) set to something not 100% (e.g. 125%), then the caret position does not reflect the cursor position. For example, with 125% if you try to highlight a line, you will see that the cursor is on line 1 but the caret position and text highlighted is on line 3.
Version tested are SL4 2012.2.725 and 2012.2.912. I hope there is a solution that does not involve upgrading to a SL5 only build.
If you have browser zoom (bottom right for IE 8) set to something not 100% (e.g. 125%), then the caret position does not reflect the cursor position. For example, with 125% if you try to highlight a line, you will see that the cursor is on line 1 but the caret position and text highlighted is on line 3.
Version tested are SL4 2012.2.725 and 2012.2.912. I hope there is a solution that does not involve upgrading to a SL5 only build.