program memory math strange behavior

[system]

uint32_t mult = index * (uint32_t) pgm_read_word_near( & NUM1024 );

...or...

uint32_t mult = (uint32_t) index * pgm_read_word_near( & NUM1024 );

...or...

uint32_t mult = (uint32_t) index * (uint32_t) pgm_read_word_near( & NUM1024 );

is this only needed for 32bit math? I never have had to do this when all constants and variables were 16bits or lower