It happened because you used Multi Camera Editing, that fixes the timelines to retain audio sync.
So when you try to drag the end of a clip you are moving the cut point (camera angles) and not adjusting the length of an individual clip.
Also notice that Ripple Editing is also applied when using MCE, again an attempt to retain audio sync.
X8 does not support MCE so saving for X8 removes the MCE effect
Thats the best i can do as an explanation, something to remember fpr next time
