Wrong SDIO settings? f_read fil only half array counts full array

Hello,

which points of SDIO (DMA) settings i have to look for if my f_read reads only half but counts full.

Example:

uint16_t buffer1[1024];

f_read(&file,&buffer1[0],1024,&cnt); 

buffer1 is filled with values to buffer1[511] but variable cnt gives me 1024

f_read(&file,&wavbuffer1[0],512,&cnt); 

buffer1 is filled with values to buffer1[255] but variable cnt gives me 512

Thanks for ideas :)