This was due to the changes that Peter recently made to the installer.
In order for the installer to be able to call the after-install proc, it must source the -procs files of the packages.
But -init files aren't loaded until *all* packages have been loaded.
Thus, developer-support would start getting called on subsequent package installs, because they check for whether the right procs are defined, which they are, because the -procs files have been loaded ... but it hadn't been initialized.
We considered two fixes, one which was to fix developer support so it doesn't do things that break if it hasn't been initialized yet. The other was to load the -init files for each package as well.
This is all a bit screwy anyway, so we chose to go the first route. The consideration was that (a) this was quick and easy to do, and (b) it's a special case for developer-support, because the mere fact that its procs exist cause it to be called by the database commands and the request processor.
All these details are meant to serve as documentation for later.
The bottom line is, it's fixed :)