that would be a bug, please report that to My Oracle Support
Noticed a bug logged on behalf of UNIVERSITE DU QUEBEC this morning. Possibly you were the originator. It was marked as a duplicate bug and the base bug fix will available in the upcoming 17.4 release. Recall that SQL Developer is now on a quarterly release cycle.
The developer comments for the fix:
The in-dialog validation for all 12.2 databases will allow long identifiers.
The DDL will fail if the COMPATIBLE flag is set to < 12.2.0.