When Rosie is talking to Izzie about the value of Pi, the Scion car in the background disappears and reappears several times.
When Izzie performs "Ironic" in front of an audience, she's wearing bright-red lipstick. Afterwards when she sits down with Dylan, at first the lipstick is visible, but keep watching and her lips are bare--keep watching and the lipstick reappears.
During a kitchen scene with Rosie and Izzie, there is a strange woman sitting at the kitchen table the entire time. They never acknowledge her, and she is never in any of the other scenes in the home.
While calculating the age differences in an inner monologue, Rosie mentions that her first writing job was for the sitcom Family Matters (1989) in 1986 when this show hadn't been developed yet.