O'Brien asks the computer for a list of ships having arrived from the Gamma Quadrant in the past weeks, the computer says there are none. However, O'Brien arrived himself back from the Gamma Quadrant.
During O'Brien's escape he goes through some Jeffries Tubes (the crawl space conduits). At the end of one of the tubes is a flat photograph or painting of more tubing to give the illusion that it continues on for a very long distance. However the picture is reused from Star Trek The Next Generation and matches the design of the USS Enterprise D's Jeffries Tubes rather than the Cardassian-built tubes of Deep Space Nine and therefore doesn't match the rest of the tubing making the transition more obvious.
When O'Brien removes his comm badge, you can see a clip or pin. In the next scene this is missing. Comm Badges are held on by a form of Velcro and don't need a pin to keep them in place.