Oh they're incredibly consistent, going so far as to retcon the one time they screwed up. Its been a major plot point for any number of episodes that matter travels through star gates one way. Remember the smoking boots scene from "prisoners" where Daniel cries "Don't they know its only one way?" Carter explicitly stated this when a student argued with her on this in the episode "Prodigy"Imperial Overlord wrote:Except they do transmissions back from malps and kinos just fine. Stargate's not terribly consistent about the whole thing. There's also a difference between saying "we knew it could be one way" and "we knew it was one way" and I honestly can't remember which one he said, leaving aside the little detail of the reliability of the source who was tad bit on the overly zealous side.Themightytom wrote: uh stargates are one way, except for that one time in "Children of the Gods" which they remastered away.
Besides the psycho Lucian leader SAID they knew it was a one way trip.
Teal'c and I think, even someone in Atlantis commented that when invading a world both the Goa'uld and the Wraith dial in to trap people there. Even in SG: U's "Air" they were worried about dialing back until Eli showed them his miniDHD worked.
If gates could be two way, they'd never have let the heart of light leave earth, they could have dialed Pegasus and let the expedition members walk back and forth. or vice versa When Atlantis had ZPMs and Earth's was depleted, they wouldn't have needed to send the Daedalus on a two week journey.
personally I always wondered if an Asgard teleportation beam could travel "usptream". It seems plausible that the hitch might not be the wormholes, but rather the stargates. If there was a built in safety feature that required only one side to disassemble and the other to reassemble at a time, and this was decided upon establishing a connection, suddenly the limitation would make sense. Its a safety feature to keep matter streams from either colliding or getting mixed together. We know the stargate is capable of doing both, it seems like either a physical constraint of womrholes, or a software issue with the Stargates.