Puzzling documentation build failure #1503

When hackage builds documentation for typed-protocols it logs the following error:

Completed    io-classes-1.10.1.0
Configuring typed-protocols-1.2.1.0...
Error: cabal: Encountered missing or private dependencies:
io-classes:{io-classes, si-timers} ==1.10.1.0

Which is puzzling, since io-classes-1.10.1.0 was built with its haddocks without errors. The full log is available here.