Its a good thought, but at this point extensive experimentation seems to indicate it's a problem with the map designer. Specifically, if the phase lanes are shown in preview, it will work in game. If they do not, it wont.
I've tried a very large range of scenarios - - the only thing that I can say for certain is that the "wormhole" option in the map designer does not work as expected. In some random maps, some of the wormholes will work (but I have yet to see one with all).
The only thing that does seem to work (but defeats the purpose of a feature in a game that - - remind me -- isn't in beta anymore?) it to only allow wormholes to be created purely by using "random mix"... which again defeats the purpose of using the map designer to customize the features of the map....
Note that I have seen some other very strange behavior in addition to wormholes that "go nowhere" including wormholes with phase lanes pointing to planets or other objects (I'm not talking about the normal phase lanes, but the wormhole phase lane which can be seen by selecting the wormhole in map preview mode). My assumption is that if you tried to use this in an actual game, it would create some sort of ugly error.
Bottom line: it's pretty clear this is a bug in the map designer. Pretty much makes random maps unusable unless one is either willing to not use wormholes, or hope that random mix will give you what you wanted.