I may have the type wrong but there is a rigid hard copper pipe which is darn near impossible to use a compression stop on without it leaking no matter how much (or little) you tighten it. And yes the pipe was clean, deburred, totally round with nothing used on the joint. I've broken those fittings trying to slowly tighten them till the leak stopped. You can anneal it with a torch, but then you risk losing a sweat fitting in the wall you couldn't see and there's not much point in using compression fittings if you have to use the torch-just sweat it on (or sweat a threaded adapter) and your done.
There's a ton of reasons I hate plumbing. And I think in 4D as well as 3D. If it were standardized to one system it wouldn't be bad, but with at least 6 types of supply piping and at least 4 types of drain piping you cannot possibly have what need on hand every time when you show up to do a repair unless your truck does only plumbing. And then you're still usually going to need another trip to the plumbing supply house.
It's getting better now that PVC is almost universal for drains and PEX is nearly there for supply. But that doesn't help when you have an old house where ten idiots have been there before you and cobbled repairs together with whatever they had on hand. And half of those idiots were in the plumbing business, just trying to avoid another trip for parts. And there's the fun of crawling in mud and water under a house all the time (more fun in the winter). Or finding somebody screwed up the electrical ground and getting the snot knocked out of you when you touched the pipe laying well-grounded and wet under there. And really, who enjoys playing around with things filled with human waste? I can't count how many times I've fixed failed joists and beams because the plumber removed material they shouldn't have, often when it wasn't necessary but that was the easy way so they did it without a care.
Yeah, I'll stick to carpentry etc as much as I can even though I can do plumbing to code, even the weird stuff like wet vents. It's water that most often damages houses, and as often as not it is failed plumbing that put the water there. If it's more than incidental plumbing I'll call a plumber, and while he's fighting all the problems I'll be clean, dry, and cruising through the rest. Just my not-so-humble approach to life in the home repair business, and see ya on the next one!
Phil