Hm...That is weird. When I close my DSi's lid, nothing happens, it just pauses. Mind show us the following?
1.What brand of a Micro SD card you are using?
2.Does it occur on all games/hombrew/in the AKAIO GUI?
3.What is your Acekard's HWID? (It's located, when you go to the Acekard GUI, and press Start. Then pressing "Help".
4.When did you buy your DSi? (I bought mine release date)