Where did you get the idea that an owner warranties a house he's sold?

Not the owner, but the manufacturer if there is still a warranty. Prior
to selling me the apartment he renovated the whole kitchen, and yes the
place was inspected. As I said, at that time joints weren't falling
apart and the wood was not bended (all doors shut properly). As someone
already pointed out it is the manufacturer's fault.

See those big filler strips where the cabinets turn the 45 degree corner?

No, I don't know what you mean.