Opens another workbook but doesn't activate it, ignores ScreenUpdating = False

I updated a .xls workbook to .xlsm. It automatically opens another workbook, Lookups.xlsx, containing a bunch of lookup tables used in numerous combo boxes and formulas.
When I open the 1st workbook, Lookups.xlsx becomes and remains the active workbook, even though the code does a ThisWorkbook.Activate. The same is true if I run Auto_Open manually. Here is the original code:

Option Explicit
Dim WorkName As String, ReadOption As Boolean
Dim WorkPath As String

Sub Auto_Open()
    Application.ScreenUpdating = False
    WorkPath = Range("PrimaryPath").Value
    WorkName = Range("LookupName").Value
    ReadOption = Range("ReadOnly").Value
    Workbooks.Open Filename:=WorkName, ReadOnly:=ReadOption
    ThisWorkbook.Activate
    Application.ScreenUpdating = True
End Sub

I tried stepping through it with the debugger. It opens Lookups, but when I hit F8 for the next step, nothing happens because the Lookups window now has the focus. If I click the debug window to put the focus back there, and then hit F8, it activates ThisWorkbook as it should.

I suspected some kind of timing issue, so I changed the code to the following:

Sub Auto_Open()
    WorkPath = Range("PrimaryPath").Value
    WorkName = Range("LookupName").Value
    ReadOption = Range("ReadOnly").Value
    Application.ScreenUpdating = False
    Workbooks.Open Filename:=WorkName, ReadOnly:=ReadOption
    Application.OnTime Now() + TimeValue("00:00:01"), "ActivateMe"
End Sub
Sub ActivateMe()
    ThisWorkbook.Activate
    Application.ScreenUpdating = True
End Sub

This solved the activation issue, but it ignores ScreenUpdating = False. This was not the case in previous versions of Excel. Does 2007/2010/2013 ignore ScreenUpdating = False when opening another workbook?

I've presented two different issues here. It would be nice to know the answers to both, but I'd settle for either one

I suspect that "thisworkbook" refers to the workbook housing the macro.

try

windows(workname).activate

Thanks for the suggestion. Actually, it would be

Windows(ThisWorkbook.Name).Activate

I tried it, but with the same results.

ScreenUpdating will be made True when first routine ends and before second routine is run. This is normal and same as previous versions.

Based on that clue, I tried the following adjustment

Sub Auto_Open()
    WorkPath = Range("PrimaryPath").Value
    WorkName = Range("LookupName").Value
    ReadOption = Range("ReadOnly").Value
    Application.ScreenUpdating = False
    Workbooks.Open Filename:=WorkName, ReadOnly:=ReadOption
    Application.Wait (Now + #12:00:01 AM#)
    Windows(ThisWorkbook.Name).Activate
End Sub

but it also didn't work. It pauses for 1 second, but leaves Lookups as the active workbook.