As has often been pointed out, the stable-kernel releases are meant to be
stable; that means they should be even more averse to ABI breaks than
mainline releases, if that is possible. This may be a hard promise to keep
for the next set of stable kernels, though, for the most mundane of
reasons: nobody thought that there would be more than 255 minor updates to
any given kernel release.

Source: LWN.net – [$] The imminent stable-version apocalypse