It appears that the “clicks” member in SDL_MouseButtonEvent, new in SDL 2.0.2, is not set correctly. After testing a pattern of usage cases I can’t see a meaningful pattern to the values it holds (e. g. 25, 140, 220) following a single or double click). My testing has been limited to Windows platform using 32-bit SDL binaries.
Update: This issue has been resolved by upgrading to SDL 2.0.3.