When Lt. Riker is late to beam back to Nervala IV and runs into the transporter room, you can see his phaser falling out of its holster onto the ground; however, in the next shot, the phaser is back in the holster.
After the bridging collapses and Lt. Riker is pulled up and crawls over Cmdr. Riker, a long shot shows that the stunt double's legs and feet haven't gotten completely out of the shot before Lt. Riker stands up.
After the two Rikers beam down to the station again, Lt. Riker crawls underneath a console and Cmdr. Riker sits in a chair to access a console. Cmdr. Riker moves the chair away from the console to talk directly to Lt. Riker, but in the shots showing the lieutenant working, Cmdr. Riker's chair is back to being positioned in front of the console.
When playing poker, Cmdr. Riker raises from 50 to 60 and later from 100 to 120.
This is not permitted.
Poker rules require any raise to be at least as much as the previous bet or raise.
So, he would have had to have raised by at least 50 in the first case and 100 in the second.
At one point, Data refers to the star as "the sun". It is done ever so often on this show; nevertheless, it is technically a "star". Data of all people should use the correct technical terms, especially when on duty on the bridge.
However, he referred to it as "the sun", not "the Sun". The star is *a* sun and is *the* sun of this system.
The first time Lieutenant Palmer beams the two Rikers back down to the station, a quick camera shot of her control console shows it to be completely blank and dark, even though she is punching buttons (which beep) and verbally confirming the coordinates, etc. she is supposedly reading on the panel.
Near the end, just after Will gives Thomas the trombone, you can clearly see that residual lipstick from Counselor Troi is on Lt. Riker's lips in the exact shade worn by Deanna. This is puzzling, since Troi never kisses him after arriving at his quarters prior to this moment. It's not until the Lieutenant is about to leave that they kiss. This is obviously from having shot multiple takes of this scene.
When Commander Riker shouts "I gave you an order..." to Lieutenant Riker, one can see where the picture is joined. It's evident at the bottom of Commander Riker's arm.
Cmdr. Riker received a promotion because of his deeds on Nervala IV. Lt. Riker performed those same deeds, and therefore deserves the same promotion, yet this is never brought up.
When they first beam down and find Lt. Riker, they decide to take him back to the Enterprise. Worf calls the Enterprise and says "two to beam up"; however, he does not define who else is beaming up with him. He also does not state that they found a second Riker. Even if the transporter operator could scan the area, there should be some confusion with scanning and finding two identical human males.
Riker's duplication doesn't really make sense. The transporter is supposed to work by transmitting matter as a particle stream. The duplication would mean that extra mass was created out of nothing.
Data has a long discussion with Worf about why someone may be upset about having a duplicate of themselves around. Data, by this time, has experienced that with his identical brother, Lore, and has had his own opinions on how uneasy it is before.
8 years before these events, Will Riker had no beard and thus Lt. Riker should also be clean-shaven. While it's possible and even likely that he didn't shave while stranded, his beard would not have looked like the commander's... it would have been a lot longer and ragged.