I came close to a failure last night, I nearly burned up my first 219b...
I built up a new P60 drop-in using one of my surplus emitters. Nothing special; Aluminum PCB, 3x 7135 single-mode driver in a 501b host. After assembling it and verifying that it all worked, I took it back apart to optimize the reflector isolation/spacer ring. On re-assembly, I let something get shorted out (not sure how) and apparently went direct-drive from the 18650.
My first thought: "Wow, that's a lot brighter!" followed by "Wait... Blue? Oops!" and a frantic power-off. Fortunately, I don't think I burned anything permanently this time, but it was close. I can't see any difference in the tint so I think I got lucky this time.