Should adjectival phrases that are hyphenated when they modify a noun, e.g. a case-sensitive password, be hyphenated when they are predicate adjectives, e.g. The password is case-sensitive?
In Britain, whilst it is 'de rigeur' in Universities to hyphenate adjectival phrases, such as 'a time-honoured custom', 'a quick-witted response', 'an egg-headed professor' etc., there seems to me no such requirement for adjectival predicates, though I tend to do so on an ad hoc basis if it feels right.I would say, if in doubt hyphenate. I don't think one would be criticised for too much hyphenation in this way. At least that seems to be the case in the UK.
Technically, no, you don't hyphenate predicate adjectives, particularly in this case since there is no ambiguity when those are separated. I would only hyphenate a predicate adjective if the two words in question could mean something other than what I intended when taken separately.
To me this is a style issue rather than grammar; but if it's professional or academic writing, it might matter to your reader(s).