An indicator that you are using a debug/development version compiled with the "DEBUG" symbol defined. (Probably you are using one of the "rc" (beta) versions announced in this forum.)
Official "stable" versions do not have these keys activated.
I'd really like to see an additonal --debug parameter for activating these keys... I know this would be a little work for holger though, but anyways...
using those 0-9 keys is excellent when testing some CE behaviour.