FOSS gamedev and creative worlds

Hi,
When I leave the inventory screen (I have to have done something in the inventory screen, just opening and closing it isn't enough) and press a number to switch tools/blocks, the key presses are ignored until after I move the mouse pointer. Once I change the direction I'm looking in, the number keys switch tool/block slots as usual. It is minor, but a little annoying.

Cheers,
Ben