You have setup scan engine to scan HTML POST data.
When the line "MIME-Version: 1.0" is missing from the data form, Malformed Container violation verdict will be triggered.
This is a known issue. Decomposer from Symantec Scan Engine is too sensitive that if "MIME-Version: 1.0" is not inserted into the HTML POST data form, Malformed Container violation will be triggered.
This issue has been fixed on version 5.2.14. Upgrade to version 5.2.14 or higher to resolve the issue.
Symantec Scan Engine 5.2.13 or lower