You appear to to have been taught that "adverb of manner" describes one kind of adverb, which should all be expected to behave alike. Nothing could be further from the truth. "Adverb" is traditionally a wastebasket category; if you weren't sure what part of speech something should be, call it an adverb.
Consequently the category has sopped up quantifiers, negatives, modals, locatives, temporals, intensifiers, and gods know what all else. Including manner, a term which applies to certain kinds of phenomena, and not to others. Manner and means are the categories traditionally questioned by how:
- Q: How did they move the mountains?
- A: with crowbars (means)
- A: very, very slowly (manner)
But not everything can have a manner. Normally we ascribe manner (and adverbs of speed like slowly or rapidly) to motion, which is how we sense time passing. When an adverb that refers to velocity is used, the sentence is interpreted to make sense of whatever motion the speaker is presupposing. In
- The book was quickly profound.
which is grammatical though nonsensical, like colorless green ideas, the strangeness is that profound is not a motion and therefore can't be quick. If you change the predicate adjective to something with a time horizon, you can get reasonable sentences like
- The book was quickly depressing.
Of course, an enormous number of predicate adjectives with time horizons are formed from old present or past participles and therefore are hard to distinguish from progressive and passive constructions, so you might not notice.