This is interesting @garyj: the ticket you pointed contains lot of great info.
Looking at the activation process in WP, defining the WP_INSTALLING constant is useful, but it’s important that other operations are not treated irregulary just to comform to an instance (such as installation) that is currently running.
Beside the main site setup for the first time, site installation thereafter should not be breaking load processes just because we need to bail the installation instance.
That I didn’t realize. Thanks for moving it to the right location.
No, not just 5.5. It’s been there for a while now, but would be great to see a fix for this.