Bug? Unable to extend edited shots on timeline

Hi.

There's an issue that is puzzling to me and I can't figure out if it's a bug or if I'm doing something to cause it without realizing.

Here's an example to help describe what I'm encountering:

1. I take a 30 second video clip (an imported video file) from the Project panel and place it on the timeline.
2. I make edits. Trim here, trim there. For the sake of this example, let's say that I edit my movie in such a way that this particular shot ends at exactly the 15 second mark of the original clip. In other words, my out cut for this particular shot is cutting out the last 15 seconds of the original clip.
3. I continue editing my movie and at some point I return to this particular shot and I decide that I want to extend the shot a bit longer. Since the original clip has 15 seconds of material following my out cut, this normally is not a problem. I can just pull on the right edge of the shot on the timeline and the shot extends to wherever I choose, up to the last frame of the original 30 second video clip.

However -- in some cases, the shot will NOT extend to the end of the original clip. It just stops short and will not allow me to extend the shot any further.

I can't explain why.

I don't know what might have been done to this particular shot to prevent it from being able to extend itself past a particular point. I'm not doing anything special. Just simple editing.

Sometimes I've run into cases where it won't extend past the exact frame where I made my cut. Other cases it allows me to extend the shot somewhat, but still will not let me extend it to very the last frame of the original clip. It just reaches a particular frame and will not go past it.

I have not been able to find a solution and I end up having to delete the shot in the timeline and replacing it with a new instance of the clip from the project panel.

Has anyone else had this happen to them?

I'm using the most recent version (I've noticed this happen in previous versions as well).