Hi,
As I understand, you have the crawled property Usage_x0020_Restriction is the same with the site column Usage_x0020_Restriction in SharePoint 2013.
I have test the issue according to the steps in your post. After doing a full crawl, I get three relative crawled properties. They are Usage_x0020_Restriction, ows_Usage_x0020_Restriction and ows_taxId_Usage_x0020_Restriction. And it only create the managed property owstaxIdUsagex0020Restriction for the crawled property ows_taxId_Usage_x0020_Restriction automatically.
You could reset the index and do a full crawl to check if the same issue will occur.
The article below is about from site column to managed property - What's up with that?
https://technet.microsoft.com/en-us/library/Dn794220.aspx
Best regards,
Sara Fan