This doesnt seeams not to work as espected
Nope, it does seem to work as expected, because you've literally simulated the initial cycle. When you erased all mediums (even the one that contained the latest virtual full backup), you made backup console unaware of point before which it should look for backup files.
When virtual full backup is created, backup console automatically memorizes its creation date. Starting from this moment, backup server won't try to copy points creation time of which is older than that date.
What happens when the tape which contains the VBK is expired and returned to the Free pool? In this case is it copied again on the next job run?
With virtual full backup enabled the oldest restore point (.vbk that is being merged on regular basis) will be copied only once. Even when tape containing it returns to Free pool, the said point wouldn't be copied, as virtual backup would be utilized, instead.
I returned the tape to free pool and next time the tape-job ran it copied full+Synthetic again.'
This isnt good when you have 50 TB data to protect.
You think this is good logic?
(Full = all vbk-files)
1. first run of tape-job = Full+Synthentic
2. Second run of tape-job= Synthetic
3. third run of tape-job= Synthetic
4. Marked all Tapes as free
5. Fourth run of tape-job= Full!!+Syntetic
but this isnt correct
"... Even when tape containing it returns to Free pool, the said point wouldn't be copied, as virtual backup would be utilized, instead..."