Today after the scrubber reverted as usual to the Timeline1 mid-point all of a sudden something changed. The very first video frame which had always been at the start of Timeline1 was appearing just beyond Timeline1 mid-point only a few frames ahead of the scrubber. I quickly saved the work file. Means I messed up something on the previous day? Was told previously the edit system can hold several hours? But as of now the Preview counter shows the edited frames at only twenty minutes long. What gives here?