I recently purchased some gems through the Moneybookers option, and right at the end of the process, the site said that the transaction had failed, before taking me back to the shop screen to start over again.
However, I was suspicious, and waited a minute or two, and sure enough, the gems came into my account, and I also received the customary 2 emails informing me that the transaction had been made successfully.
So, if it does appear to fail, check first to see if the things come through, otherwise you could easily make a pointless and expensive duplicate purchase.

Ticket raised for Support to look into this process.