How to open the case for HUMAX RM-F01 Remote control to the iHDR-5050?

How to open the case for HUMAX RM-F01 Remote control to the iHDR-5050?

The remote control has gathered dirt which has led to keys that need quite a lot of force to be activated. I'd like to clean it up, but I simply cannot open the case. There are no screws, no clips, nothing. The battery compartment doesn't reveal anything either. It looks and feels as if it has been glued together, but that doesn't make sense.