After five months' closure, the Waterloo & City line reopened last week, and immediately ran into trouble.
The cabling was incompatible with the signals, causing surges. The Correct Side Door Enabling kit didn't work. There were power feed problems - all of which should have been sorted through a testing process before the line reopened, you'd think. Passengers who've already had five months' inconvenience don't usually take too kindly to a line breaking down as soon as it reopens.
It all adds up to grief for the signallers, drivers and station staff.
Hey - perhaps if refurbs were done by an integrated, publicly-owned London Underground engineering department, then you wouldn't have private contractors cutting corners and cocking up. Now there's an idea ...