Other mistake: The Sliders discover the reverse-time issue when they notice that the clock on the wall is backward. However, in other shots, clocks look normal. Look carefully at the clocks on the judge's desk as the camera pans by.
The Debt (2) - S3-E7
Other mistake: At the end when it shows that Xena did kill the "green dragon", you can see his eyes move when the camera pans around his face to show the hair clip in his temple.
Free Spirit - S7-E13
Other mistake: The storm has knocked out power to the facility, the emergency generator did not engage the supply power and is out of fuel, but in some parts of the building there are lights on.