Continuity mistake: Season 4 - Episode 8 - The Earth Girls Are Easy - When Kaitlin is at the party, talking to Bullit, her strand of hair changes from hanging over her eye to hanging down next to it, without her moving her hands or head to displace it.
Continuity mistake: Season 4 Episode 5 The Sleeping Beauty: When Taylor calls Ryan in the middle of the night (around 03:03 when he first checks), the second time Ryan checks the time on his radio it shows 03:23, however it jumps back to 03:04 when he looks again.
Revealing mistake: When the limo pulls up to the hot dog stand, Julie steps out from the back seat. And as she walks toward Frank standing in front of the picnic tables, the limo driver is visible behind the wheel. Julie joins Frank at a table, and then Ryan decides to enjoy a last spin in the limo telling Taylor they've rented it for 2 more hours. In the next shot they are sitting in the front seat talking while Ryan is at the wheel, when the limo driver never left the vehicle. (00:41:20 - 00:42:46)