The expression VALUES ('cd' SIMILAR TO '[a-e^c]d') returns TRUE. It should return FALSE.

SQL:2008 spec has a general rule for SIMILAR predicates:

l) L( <left bracket> <character enumeration include> <circumflex> <character enumeration exclude>
<right bracket> )
is the set of all strings of length 1 (one) taken from the set of characters in the <character enumeration
include>s, except for those strings of length 1 (one) taken from the set of characters in the <character
enumeration exclude>.