Ascii 'F' being added to SD card data

AL-FAT SD module. Purchased Jan 2016.

When I flush a group of data to the SD card , an ‘F’ is included in the saved data. It is not part of the data and does not occur until the 3rd flush command is sent, and any other flushes of data.
The 1st two flushes do not show the extra character.
I suspect it might be the ‘F’ in the flush command itself.
I open file to write.
Send write command with the number of bytes.
Send data bytes…I get correct response when complete number of bytes are sent.
Send flush command.
Repeat the process.

Anyone ever see this occurrence?
Regards
Bill S

Never heard of this before.

@ billghi1 - So we can test, can you send us the minimal commands to run to reproduce the issue?

Found the problem
I had my “write data” command off by one byte . I had the byte count 1 too many.
"W 1>24\r"
Then when the flush command
"F 1\r
was sent it used the ‘F’ for the last byte it needed and also used it as the flush command. So the ‘F’ was added to my data string.
Changing to “W 1>23\r” fixed the problem.