When Barclay is just about to return from the Yosemite, his rank insignia is the wrong way round. It should be black then gold. However, it is gold then black.
This episode marks the beginning of the controversy regarding O'Brien's rank. Up until now, he had worn the insignia of a Lieutenant. Since one scene in the transporter room requires Barclay to give O'Brien an order, the producers had to suddenly change O'Brien's rank to something less than Barclay's (which was Lieutenant Junior Grade). They chose to make him an Ensign Junior Grade, which is a rank that does not exist. Eventually his rank insignia would evolve into that of Chief Petty Officer, but it took over a year and a transfer to Deep Space Nine. It would have been much less confusing to just have had a lower ranking character manning the transporter room.
Barclay asks La Forge "Commander, has anything strange ever happened to you during transport... anything out of the ordinary?" La Forge answers "No, not really." However, in the previous season La Forge and Ro Laren are involved in a transporter accident in which they are both presumed dead (but in fact are out of phase with normal matter). This would certainly be considered strange.
Barclay gives O'Brien an order in the transporter room. But O'Brien didn't have to follow it, because at that stage in the story, Barclay's been relieved of duty. However, it is possible that O'Brien isn't aware of it yet, seeing as it was a decision by the counselor.
Though a force field had been erected around the transporter chamber, a re-materializing crew member's leg falls outside the pad before the field is dropped.
Microphone visible for a few seconds above Data and Geordi when they are setting up the plasma experiment in Engineering.
When Barclay queries the Computer about transporter psychosis, she keeps referring to people who have it as "victims". Since it is a mental disorder, they would be referred to as "patients" in a medical database or textbook, especially in the enlightened future of the TNG universe.