Endianess on STM32F4 FSMC output
You are writing to an odd address (0x63FFF00F) using 16 bits. That might explain the surprising result. – Codo


Codo was correct. Accessing odd bytes while the FSMC was configured for 16bit datawords made it do a double access ( 2 write operations) with the bytes in exactly the wrong order.

My adresses are now: 

#define LCD_CMD 0x60030000
#define LCD_DATA 0x60000000