Hi e-bradley,
This is a software defect, and affects all models of ASA hardware both -X and non-X, including the 5520. Additionally, 8.4 and later versions are impacted.
However, the bug is "minor" as it is reported to only be a cosmetic error, and not actually affecting the login via SSH. If this is incorrect, I would request you open a TAC case and we can gather more details, reproduce and increase the severit of the bug.
Thanks in advance,
David White.