[koenigdavidmj]

Sounds like they learned their release numbering skills from the KDE folks.

[rtaycher]

I'm not sure if they do it but many projects use odd=unstable,even=stable version schemes including GNOME.

[JoachimSchipper]

Yes, but that's usually in the second digit (e.g. 2.4 is stable, 2.5 is development) - switching from unstable to stable in a nominal patch release (third digit) is at least uncommon.