Problem with synthetic's backup

I try to use synthetic backup for an ordinary windows file server.

I've created MS-Windows type policy.

Checked attributes "Collected true image restore information" and "with move detection".

Сheckedthe presence ofthe flag "OptimizedImage" for storage server and deduplication pool (via "/nbdevquery -liststs" and "nbdevquery -listdp").

I've created for this policy the necessary Full backup and Cumulative backup schedules.

But when I try to created Full Synthetic backup schedule I can't to check "Synthetic backup" attribute (look to attached screenshot).

What am I doing wrong?