I think you mean LSUIElement in Info.plist.
Anyhow, what you say is true, and I have set LSUIElement in BookMacster's Info.plist, and when I want it to launch in the background I do not transform the process and everything is fine. The problem is when I want BookMacster to launch in the foreground. That is when I transform it to foreground, and Finder flashes momentarily. Of course, this is not noticeable when BookMacster is launched from Finder, as it usually is, so maybe this is acceptable, but I don't like it.
In case the above is confusing, I shall digress a little. BookMacster has a Launch in Background user preference. Of course, by default it is off, because otherwise new users would never see the app. It is in fact only available if the companion Show status in menu bar preference is enabled. The users and use cases for Launch in Background are in the minority, but significant.
Now there are two mirror-image approaches to implementing a Launch in Background user preference. The first approach is to set LSUIElement in Info.plist and, during launch, do nothing if the preference is background, or transform to foreground if the preference is foreground. The second approach is to not set LSUIElement and, during launch, do nothing if the preference is foreground, transform if the preference is background.
I use the first approach because transforming to background is not supported in Mac OS X 10.6. (*) I think you're telling me that this first approach is also used in Alfred, but Alfred does not have a Launch in Background preference setting. It's hard-wired to be an LSUIElement (background), and comes to the fore only when user clicks the gear.
* * *
While I'm thinking about this, I'm still curious, Andrew, about my original question - does Alfred use some tricky method for launching apps which is not in the list in my first post? If not, that is, if Alfred uses, as I would, one of the conventional NSWorkspace methods, then maybe the significant factor is the fact that Alfred itself is a background app, and the stealth bug fix which Apple did in Mavericks only works if the "launching app" (I'm not sure what that means because the actual launching is apparently done by launchd) is itself in the foreground. Note that, in contrast to Alfred, LaunchBar is a foreground app. It appears in the dock, app switcher, has a menu, etc.
Thanks,
Jerry
(*) Yeah, I know, another reason to drop support for 10.6.