Extra bytes are getting released from reservedSpace for append

1. File already have some bytes available in block. (ex: 1024B)
2. Re-open the file for append, (Here reserving for (BlockSize-1024) bytes)
3. write one byte and flush,
4. close()

After close(), releasing BlockSize-1 bytes from reservedspace instead of BlockSize-1025 bytes.
Extra bytes released from reservedSpace may create problem for other writers.