BSWAP EAX converts from little endian to big endian and vice versa. It was a 32 bit instruction to begin with.
However, we have the 0x66 prefix that switches between 16 and 32 bit mode. If you apply that to BSWAP EAX undefined funky things happen.
On some CPU architectures (Intel vs. AMD) the prefix was just ignored. On others it did something that I call an "inner swap". E.g. in your four bytes that are stored in EAX byte 1 and 2 are swapped.
0x11223344 became 0x11332244.