Parts of Speech

Asitwas

Interestingly, unlike the central cases of conversion, it is not the lexical base that is converted here but an inflected form.

And derivation doesn't really occur to inflectional forms in English (does it?), so I doubt that words to which -ing and -ed suffixes have been attached and are not considered as verbs are considered as converted forms.

Also, inflectional suffixes -ed and -ing can be attached to verbs only. Given the fact that -ing and -ed suffixes are also found to be attached to some nouns and create new words (e.g. detailed, dogged, roofing, clothing, etc.), I think treating them as derivational morphemes is a better approach.

The process I referred to has it in common with uncontroversial cases of conversion that we have homonymous pairs of words of different primary categories.

To talk of morphology here presupposes that one already knows (or has a good idea of) the word class of the items in question. This is not the case here -- the humble OP does not know what word class "suffering" belongs in, hence their question the answer to which is provided by the tests I cited, which provide solid evidence to support the categorisation of the words concerned.