MarketPress not allowing decimals

Hey, getting a weird glitch on boaztrust.org.uk where it doesn't allow £2.50.

We want to set http://boaztrust.org.uk/store/products/christmas-cards/ to £2.50, but it on save it rounds it up to £3.

How do I resolve this? Latest WP, latest MP, etc.

Bless,
Chris