WiX will not uninstall due to conditions in CustomAction - wix

Question

I have an MSI that uses two CustomActions. The first adds some stuff to the registry. It runs every time except during uninstall. The second removes a key from the registry to be run only during uninstall.
Both CustomActions work fine, only now the MSI won't uninstall.
By "it won't uninstall" I mean neither the file that is installed is deleted nor is the MSI removed from Programs and Features when uninstall is run. The only thing is does do during uninstallation is the Custom Action that removes stuff from the registry.
Note that the problem happens on a fresh Virtual Machine, so it's not like there are old versions with different GUIDs hanging around.
Also I don't think that there's a problem with the Features, as there's only one feature -- a textfile installation (it's a toy installation -- until I get this right it's not going in the real installer).
Here is the <InstallExecutiveSequence> code from both Custom Actions. The one where I put stuff into the registry, to be done every time except uninstall:
<InstallExecuteSequence>
<Custom Action="CustomAction_CreateKey"
After="InstallInitialize">
</Custom>
</InstallExecuteSequence>
And here is the same XML from where I delete from the registry, to be done only during uninstallation:
<InstallExecuteSequence>
<Custom Action="CustomAction_DeleteKey"
After="InstallInitialize">
(NOT UPGRADINGPRODUCTCODE) AND (REMOVE="ALL")
</Custom>
</InstallExecuteSequence>
The uninstall logs aren't that helpful (at least, to me). There's this:
MSI (s) (BC:6C) [15:27:15:733]: Note: 1: 1725
MSI (s) (BC:6C) [15:27:15:733]: Note: 1: 2205 2: 3: Error
MSI (s) (BC:6C) [15:27:15:733]: Note: 1: 2228 2: 3: Error 4: SELECT
Message FROM Error WHERE Error = 1725
MSI (s) (BC:6C) [15:27:15:733]: Note: 1: 2205 2: 3: Error
MSI (s) (BC:6C) [15:27:15:733]: Note: 1: 2228 2: 3: Error 4: SELECT
Message FROM Error WHERE Error = 1709
MSI (s) (BC:6C) [15:27:15:733]: Product: CustomActionDeleteKeySetup --
Removal failed.
And this:
Calling custom action DeleteKey!DeleteKey.CustomActions.DeleteTheKey
Exception thrown by custom action:
System.Reflection.TargetInvocationException: Exception has been thrown
by the target of an invocation. --->
Microsoft.Deployment.WindowsInstaller.InstallerException: Cannot
access session details from a non-immediate custom action
at
Microsoft.Deployment.WindowsInstaller.Session.ValidateSessionAccess()
at Microsoft.Deployment.WindowsInstaller.Session.set_Item(String
property, String value)
at DeleteKey.CustomActions.DeleteTheKey(Session session)
--- End of inner exception stack trace ---
I'm not really sure what to look for in the log files.
To sum up: Custom Actions won't let me uninstall. I'm pulling my hair out.
EDIT
I managed to get it working, but I don't know why. It has something to do with the conditions.
The conditions were this: when uninstalling and only uninstalling, I wanted to remove the key. So -- as shown above -- here's the <InstallExecuteSequence> code:
<InstallExecuteSequence>
<Custom Action="CustomAction_DeleteKey"
After="InstallInitialize">
(NOT UPGRADINGPRODUCTCODE) AND (REMOVE="ALL")
</Custom>
</InstallExecuteSequence>
And then I wanted to create the key when doing everything except installing. Before, I didn't have any conditions in the <InstallExecuteSequence> bit, but when I change it to this, it seems to work (that is, the custom actions work and it uninstalls):
<InstallExecuteSequence>
<Custom Action="CustomAction_CreateKey"
After="InstallInitialize">
(NOT installed) OR (CHANGE) OR (REPAIR)
</Custom>
</InstallExecuteSequence>
The question is: why does it work? Is it because earlier I was trying to run both Custom Actions during uninstallation?