We have noticed selective behavior with SED Version 10.4.1 MP2HF2 build 824 and MS KB 4074598 (February Security update).
The issue seems to only with MS Excel files using Shared Excel workbooks.
We have Isolated the issue down to:
Updates installed: If both SED build 824 and KB4074598 are installed, the file appears as corrupt.
OS: Windows 7 and Windows 2008 R2
Files: MS Excel XLS files or XLSX
Is a Shared Workbook
Located on file server
Encrypted and not Encrypted files same behavior
Due to a change on the MySymantec Support page I cannot open case.