This was a glitch introduced in Rayman Origins Demo for 3DS(only found by golumitu.if in final post here) . Its allows you to get Lums at a respawn check. This can be only done in the first level though.

All you have to do is die while the coin releases Lums.When respawning you'll have a number of Lums other than zero.This glitch was confirmed by Golumitu accidently.