I have a 32GB Lexas Micro SD card in my Samsung Galaxy S2 i9100. For some reason, the card consistently shows 12gb as the size of the card. It just randomly started doing this about 2 weeks ago.
I have done an on-device format (as it has prompted me once or twice to format), a format with an SD card utility through the SD card group, and a Windows formatting. It still shows 12GB.