Get-Help -Online in 5.0 opens core cmdlet help for 4.0
For the core modules in PowerShell 5.0, Get-Help -Online opens the help for PowerShell 4.0, not for PowerShell 5.0. Typically, -online gets help for the latest version of the module by default.
For example: Get-Help Import-Module -Online
...opens "https://technet.microsoft.com/library/af616c24-e122-4098-930e-1e3ea2080ade(v=wps.630).aspx", the 4.0 version of help.
That's because the first related link in the XML help topic has the FWLink for the 4.0 topic.
I suspect this is a bug caused by an incomplete understanding of how -Online works. The tool (or person?) that was supposed to update the links for 5.0 didn't know how it worked and updated only the HelpUri attribute.
The URI for online help can be added in one of two places:
-- First related link of cmdlet/function help
-- HelpUri attribute of the cmdlet
When both are populated, the first related link takes precedence.
For core cmdlets, the URI in the first related link is the URI to the PowerShell 4.0 version of the help topic. For example:
The link to the Import-Module help for PowerShell 5.0 is the value of the HelpUri attribute of the cmdlet.
We should fix this and make sure that the tools for 6.0 do it right.
This should be fixed in 5.0 and 5.1. If not, definitely let us know.