When Ishara is describing the Alliance fusion source to Data on the bridge, she points to the computer to show him the locations of various entry points to a specific chamber on the cartographic display. In the reflection on the monitor, you can very clearly see that Ishara's lips are not moving as she continues to speak. Furthermore, the actors portraying both Data and Ishara appear to be possible stand-ins for Brent Spiner and Beth Toussaint respectively.
When Dr. Crusher takes a DNA sample from Ishara, she says the test to see if Ishara is related to Tasha will take a few hours. However, other instances of DNA being analysed had nearly instantaneous results.
When talking to Ishara on the bridge, Data talks about Tasha becoming close to "myself". Grammatically this is incorrect, he should have said "me" as he is the object pronoun. For someone who is impeccable in language including lack of contractions, this is an odd mistake.
When Riker's away team first encounters the Coalition raiders, he states that they're from the USS Enterprise and that they're looking for two of "our" crewmen. The men they are rescuing are from the Federation freighter Arcos; they are not from the Enterprise.
At one point, Picard refers to Hayne's coalition as "Haynes's coalition".
On the bridge near the end of the episode, Picard says that each of them was to blame for being so willingly deceived, apparently forgetting that Troi had twice warned him of a deception.