Failure in file-source loopback test with packet encoder/decoder

Hello all–

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Last commit: b52a6f36d76012951b72ad07277664bbc07d57cd

I am attempting a loopback test using the packet encoder/decoder and a
different modulation schemes (QAM for this specific example).

Upon attempting to source a file generated to align to the configured
payload size, the output is still short a few bytes. Different
produces the same results.

-rw-rw-r-- 1 user user 256000 May 2 00:51 in
-rw-rw-r-- 1 user user 254976 May 2 01:12 out

Any thoughts for narrowing this down? Code is here:

Thanks in advance,

Trying again. Is this normal?