When I shelve only one thing, am I not putting it on one shelf?

Whenever a verb and a noun are basically the same word, there is sometimes a tendency to differentiate their pronunciation. This can be done by shifting stress from one syllable to another: compare they will convict him with he is a convict. It can also be done by pronouncing a fricative (s, z, f, v) voiced (z, v) instead of voiceless (s, f): compare that is no use with I can't use that.

The spelling shelve as opposed to shelf has little to do with the plural of the noun: it is just a marker of pronunciation. Because /fs/ is quite unusual in English, the plural shelves happens to be pronounced with a voiced fricative (v), which happens to be represented by its spelling.