I was double charged Avios by BA, basically what happened was this:

We were in CDG, missed our flight and facing the prospect of change fees or buying a new flight the agent advised us that given that Avios seats were available, we should try booking that.

I did so, selecting the Paypal option for payment, booking from my mobile phone. After submitting payment, the BA website said 'Our systems are not responding, try again', or words to that effect.

So I did.

I have now realised that in fact two bookings were made, and two sets of miles charged.

I assume that this is a problem with the interaction between Paypal and BA.com, but anyway it's pretty annoying....