Constantine I Arles campgate with unusual top row

[Victor]

This campgate has a very unusual top row. I initially though that it must be unofficial, but other than the strange top row of the campgate, it looks official.

Constantine I
A.D. 328
19mm    2.8gm
CONSTAN-TINVS AVG; pearl-diademed head.
VIRTV-S AVGG; gateway with wide open doors, four turrets, star above. S/F in fields.
in ex. SCONST
RIC VII Arles 321

[tjaart]

That is a nice variation!

[Genio popvli romani]

Is it the explanation for the price it sold?
Here is another specimen from different die : http://www.nummus-bible-database.com/monnaie-54113.htm
There are also a few specimens of Arles 321 from 1st officina with the same kind of upper row design : http://www.nummus-bible-database.com/monnaie-25163.htm

[Victor]

Is it the explanation for the price it sold?

I can only assume that is why so many were interested.