This made me think, there's M, L & K copper pipe. They all have the same OD, but different ID, correct?
The only other thing I can think of is that the pipe swelled for some reason.
Of course, my only plumbing experience (other than DIY projects) was working in the plumbing department at Payless Cashways in college (man, you get some weird requests, then there's the kids that can't make it to the store bathroom......."where's the TP?".... ugh!!) and my current position as a CAD draftsman for a MEP Engineering firm working on the mechanical side of things, mainly plumbing and chilled/heating water systems (just finished a central plant addition for a university that had two 5000 tonne chillers piped with 18", 20", 24" and 30" piping, that was fun to draft!!!)
Larry Hampton