The English suffix -some is not the same as the adjective some, which means an unspecified quantity. The suffix -some means causing, or characterized by. Quirksome is not in any of my dictionaries, but here are some words that are:

awesome
burdensome
cuddlesome
fearsome
gladsome
irksome
loathsome
meddlesome
quarrelsome
tiresome
toilsome
troublesome
wearisome
worrisome

And here are a few more that need some explaining:

fulsome – can have a positive or a negative connotation. Fulsome praise may mean abundant praise or it may mean overdone praise.
gruesome – in the Scots tongue, grue means to shudder.
handsome – the original meaning was “easily handled”. Over time it has morphed into meaning good-looking, attractive, or generous (as in a handsome financial gift or settlement).
noisome – As a child I couldn’t understand how a pestilence could be noisy. In time I accepted that noisome meant something else. Finally I checked the dictionary and found that the prefix noi- came from annoying. Thus a noisome pestilence is a disease epidemic that produces the annoying stench of sickness and death.

I’m sure you philologists (word-lovers) out there can add to my list.