Multiserver APS Installer Issue
In a multiserver setup, the APS installer - in "aps_guicontroller.inc.php" - checks to see if the web server that the package is going to be installed on is also a DB server and, if it is, then it uses "localhost" as the DB host (line 249 - it's a hard-coded string).
The problem is that whilst that would be correct for the web server itself, "localhost" would be incorrect for other servers in the multiserver setup. E.g. a mirrored server and / or using shared storage.
So, really, the DB host ought to be the IP address of the DB server, instead of "localhost", so that it remains correct from the perspective of all servers (I've hard-coded the IP address into my own setup and, yes, this seems to work okay, as far as I've tested it - but it would obviously be better if ISPC itself did this, so it'd be generically correct for everyone's setup).
(This produced a weird bug in my load balanced / shared storage setup, leading to the website working or not working, depending on which server was selected by the load balancer. Which was confusing when, on my machine, thanks to persistence, it worked just fine but then it did or didn't work for others in a seemingly random way - and it took me a while to work out what was causing this. But it's because the DB config was right for the one machine that I installed it on, but not for the others.)