Opera (version 12.x, I have to install a new one at some point)
 In a topic,
 Quick reply "plaintext"
 Quote a message
=> javascript error in this function:
function replaceText(a, b) {
	if ("caretPos" in b && "createTextRange" in b) {
		var c = b.caretPos;
		c.text = " " == c.text.charAt(c.text.length - 1) ? a + " " : a;
		c.select()
	}
	else if ("selectionStart" in b) {
		var c = b.value.substr(0, b.selectionStart),
			d = b.value.substr(b.selectionEnd),
			e = b.scrollTop;
		b.value = c + a + d;
		b.setSelectionRange && (b.focus(), d = is_opera ? a.match(/\n/g).length : 0, b.setSelectionRange(c.length + a.length + d, c.length + a.length + d));
The error is at this piece:
a.match(/\n/g).length
and the error is:
Unhandled Error: Cannot convert 'a.match(/\n/g)' to object
Though, it seems the error appears only quoting one of the (broken) messages in this topic:
http://www.elkarte.net/index.php?topic=508.0
not the last one by Shawn.
Probably related to some wrong encoding somewhere...
Test °C