@Pinoykolokoy
Thanks, but there's an exception to that grammar rule. You can't always make generalization based on limited sample size. Aside from that, Tagalog language is both inflectional and derivational. For example, noun + suffix -in also denotes place.
Ex:
1. Bukid + in = bukirin
There's no bukiran
2. Lupa + in = lupain
There's no Tagalog word lupaan
* Ka + root word (noun) + an could also mean abstract quality.
Ex:
Root: lupa
ka+ lupa+ an = kalupaan
Meaning:
1. Land mass
2. worldliness; earthily characteristic (same meaning with kamunduhan from root word, mundo)
* Your example "damuhan" (damo + suffix -an) doesn't only function as a noun but also as a verb.
Ex:
1. Damo (root word) - noun
A. 'Wag kang umupo sa damuhan.
Damuhan - refers to a place (noun - inflectional)
B. 'Wag mong damuhan ang harapan ng bahay.
Damuhan - denotes action (verb -derivational)
2. Bato - noun
A. 'Maglagay ka ng tent sa batuhan.
Batuhan - place (noun)
B. Away magpinsan nauwi sa batuhan ng bote.
C. Batuhan ng linya
Batuhan (does not refer to a place or location but more of a reciprocal noun)
D. Batuhan mo nga ako ng isang mansanas.
Batuhan - verb