The BTunes and all Bluetooth devices experience some form of lag/latency. For the BTunes the transmitting device has to encode the audio to a format that can be sent over bluetooth, the signal has to reach BTunes, and finally the BTunes has to decode that signal. All of this gives the BTunes around 120-150 milliseconds of delay.
While listening to music this delay does not make much of a difference. However, when you are watching video/movies the delay can cause the sound and lip movements from actors to become out of sync and make it feel like you are watching an old Chinese Martial Arts movie. How much delay you experience depends heavily on what program or what device you are using to watch the video. For some programs/devices they take into account the lag and automatically compensate by playing the audio ahead of the video by a few hundred milliseconds.
Interference from other 2.5 ghz electrical devices can also cause delays for a bluetooth device. If the device is close to other devices that use radio frequencies (such as microwave ovens, cordless phones, remote controls for electronics or lighting, or 802.11 wireless networks), those devices might be creating interference. Try moving the device that isn't working farther away from the other devices.
There are some things you can try to correct this lag yourself. If you are playing videos from a computer, most video players allow you to change the audio/video offset so you can set it to play the audio earlier. If you are watching the video on Netflix on PC or Mac, you can adjust the video/audio sync on Netflix to get it to resynced. to do this: On Windows press Shift + Alt and hold it while you left-mouse-click on the screen. In OS X, press Shift + Option, and left mouse click. A diagnostic window will pop up with various settings and options. On there go to the audio/visual sync compensation menu and you can adjust and compensate for any sync issues.