"New game" disabled, even with levels available

[pianosaurus]

When I select Hard first, then switch board size to 16x16, the "New game" button is disabled with the text "This game combination is currently not". There are 20 levels available.

Switching difficulty to anything else then back to Hard resolves the issue, and I can start the game.

There are 0 levels available on Moderate, so maybe it's checking the level availability using the wrong difficulty (when switching board size)?