It seems that UltraEdit's single- and multi-line handling of regex is spotty/non-standard.
You could try setting the regex mode to Perl
or Unix
and using your original expression.
Also, if you copy-pasted your UE expression to the question instead of typing it manually and making a typo, then it is incorrect. You are checking for &\na\no\ns\n;
instead of &\na\np\no\ns\n;
(you forgot the literal p). It should be
&^{^p^}^^{^p^}^^^{^p^}^^{^p^}^{;^}