Setting App Firewall Rules via the API fails immediately after PortGroup Namespace change

[jmedd]

vCNS 5.5

On a freshly created DVPortGroup I can successfully change the Namespace via the API to Independent to (among other things) enable the App Firewall. If I then immediately send another API call to update the default App Firewall Rule from Any Any Allow to Any Any Deny it fails with:

HTTP 412 "A specified pre-condition has failed for this request"

If instead I leave a gap in time between the two requests the second request is then successful. So for example:

Change PortGroup Namespace to Independent

Pause 1 min (I haven't tested any lower than this yet)

Amend Default Firewall Rule

I don't really want to leave the Pause in there so have tried:

Change PortGroup Namespace to Independent

Test PortGroup Namespace is Independent

if (Independent){

     Amend Default Firewall Rule

}

which still fails.

Any idea why I have to leave a time gap after the Portgroup Namespace change to Independent?