When I select a block of text and type a new string, the selected text is deleted from all the rows that the selection covers, but the new text is only inserted in the first line.
For example if I select the block
bbb in aaabbbccc bbb aaabbbccc bbb aaabbbccc
then type xxx
I expect it to become
but instead it becomes
Is there some property I need to change in order for it to work the way other applications work?
(Note that I verified this in your Syntax editor demo app just in case it was caused by something my own app does.)