Tested with Gwiddy (FOR SCIENCE!) - tried to post The Easter Fuggly for 8b. Even with all the necessary cash on hand (and well under the 25 item selling limit) - the error message was 

15:47:50 - Failed to list items, you may have hit your Active Offers limit

As you can see I have the cash on hand. I vaguely recall an issue when people started listing things for 100m or 1b (I forget which) - to do with the type of field in the database but I may be mistaken on that.

Just tried listing it for 1b and it works successfully so suspect database field issue here.

15:50:31 - Successfully listed x1 The Easter Fuggly for a total of £1,000,000,000

I can reproduce this one easily, taking a look.

I have a PR up to fix this. KWYY your hunch is correct :)

This should be resolved now.

On my end by typing in 1k deleting it and tying 1k again its still multiplying it to 1m and so on. Both with safe and just entering price value into the market.