Prior to 5.1 (or maybe earlier), when results containing objects were displayed, the name of the field was displayed - e.g. VerifiedDomains in the example below.
There are some tricks about the formatting system. This isn’t a ‘behavior change,’ per se - it’s how the thing works.
If it isn’t given a predefined formatting view (from a .ps1xml file), it uses property names (they’re technically not “fields”). If it is given a formatting view, then it uses whatever’s defined in that view. That’s why you see column. headers in Get-EventLog output, for example, which aren’t property names.
So at some point you wound up with a formatting view for that object type, and PowerShell is displaying it. Either that, or you had one before, and a module update or something -changed- the formatting view to what you see now. Get-Member is the One True Way to see the actual property names; tables are meant as a view, not as a canonical source of programming information. Much like in a report, tables may “prettify” things. And it happens on a lot of objects you may just have never noticed.
Thanks - it’s the first time I’ve noticed it with the AzureAD cmdlets, so there probably has been a change in the AzureAD module formatting view - Get-Member it is then.