Composer update not updating alpha to beta

Hi,

I kept getting emails from one of my sites saying there were updates available - in my composer.json I've got "~1.0" set so it should pick up the latest version but it's not recognising the beta. Every other module's working fine so I asked around on twitter - @hussainweb said:

did they add a composer.json after alpha? If it's corrupt, it won't be picked up. That's the reason colorbox 1.2 is not picked

So I thought I'd note it here in case it's an issue, I can't see how it's anything else but maybe I'm wrong!

Cheers