powershell sort-object doesn't work as expected

I tried to use sort-object cmdlet to sort processes by Id's here:

Get-Process | Sort-Object -Property Id

and it works well. In any other example I found, sorting works fine, but when I try to sort employees by their employeeID from Active Directory with this one-liner:

Get-QADUser -IncludeAllProperties -SerializeValues | ? {?_.Mail} | select employeeID | sort-object -property employeeID

I get something like this:

11
1104
1105
1185
119
12
...