I have exactly the same issue, however I’m also confident that its working correctly.
I have symantec system centre v5 installed on my server this also reports the definition dates as blank.
However on my PC, I run client version 18.104.22.1689. I have also installed ssc v5 and it reports that all my clients have the correct and up to date definitions.
We currently dont/havent paid any subscription. I guess the best way to solve it would be to spend some cash.
By JimmyIT _______________________________
This maintenance Release just came out that addresses it
“Client UI would not display new definition date
Fix ID: 1171767 Symptom: On Windows Vista, SEP Client UI would not update virus definition date after they were downloaded Solution: Modified check for VirusDefs so that the directory change notification was received correctly”