Same here with Galaxy Tablet 2 7.0... 32GB SD-card is showing as 12GB, same as internal memory.
Odd thing is though... when I try with my Galaxy Y Duos, it shows correctly.
But as sroot pointed out before, might be a mounting issue. On the Galaxy Y the SD-card is simply mounted as SD and the system is..well "System". Tab internal memory is mounted as SDcard, external card as ExtSDcard.. Damn you Samsung
@-)