I'm not sure that 11 KB is enough for Windows to function.
You might want to see if f_mkfs() can create an image for windows to recognize, or if that fails or refuses.
If it is not the impractically small size that Windows objects to, it might be that the writes/reads in the format process fail in some way, or return the wrong/unexpected data.
In debugging MSC the general rule would be to instrument the interactions, and to CRC data blocks so the logs can be audited and basic functionality validated. With relatively low block counts the CRC for all blocks could be sanity checked dynamically to catch issues.
