Its not exactly "mind reading" to presume that someone wants a single row pasted into every row of a multi-line selection. An option being required to turn off this behavior? If you really want to paste to a single line to a single row then don't do a multi-line select beforehand - simply put the cursor where you want and paste it like normal.
I realize this enhancement request probably won't get implemented anytime soon, but it would save people time - at the moment to repeat a single row to multi-line paste selection semi-quickly I count the number of lines to paste to, then open up a new scratch tab, type in what I want pasted, hit Ctrl-d (copy line) for the amount of lines to paste to, copy the text, make the multi-line select, then paste, then close my opened scratch tab. Instead of - not counting the number of lines - simply selecting the text, copying it then doing a multi-line select, pasting it to all rows.