Code below will fail due to white space in the beginning of the string:

$("\\n<div/>");

Same goes for \\t and \\r. That's all I tried so far.

My original code had a multiline string with HTML code but the example above is essentially the same thing.

It looks like this bug was introduced in 1.9.0

I tracked it down to the regex in rquickExpr

In 1.8.3 it was

rquickExpr = /^(?:[^#<]*(<[\\w\\W]+>)[^>]*$|#([\\w\\-]*)$)/,

and in 1.9.0 it became

rquickExpr = /^(?:(<[\\w\\W]+>)[^>]*|#([\\w-]*))$/