Strings that begin with a whitespace will cause appendTo() to fail. This applies to both 1.9.1 and 2.x. Previous versions didn't have this issue.

E.x:

http://jsfiddle.net/4ZBdZ/1/

// This will pass!
$('<h1>PASS</h1>').appendTo('#myDiv');

// This will fail due to string starting with whitespace
$(' <h1>FAIL!  String begins with whitespace!</h1>').appendTo('#myDiv');