New images, audio, text boxes NOT added at Playhead, adding hundreds of seconds to slide

I noticed this just yesterday. Suddenly my slides were up to 454 seconds long, after I'd added a new image, audio, or text. I'm accustomed to new items being added right at the Playhead, so I set it to were I want a new image to appear. But instead, images were just added about 5 seconds prior to the end of the audio file, and they were 140 seconds long! I had to move them to the Playhead, then drag the length of the slide all the way back to the end of the audio. 

This is NOT a new occurance, but it is far worse than it ever was. I believe an easy fix, and one I've been wanting to ask for previously, is a lock on the LENGTH of a slide - once I've added the audio, and allowed a second of dead air at the end, I want to LOCK the length of the slide and NOTHING will move it a fraction of a second to the right. If I try to add in an audio or video file that is too long, the system can throw a warning and I can act on it, but I spend far too much time with Storyline 360 dragging the damn slider from some incredible length out so that my brand new slide isn't 8 minutes or so long when it's supposed to be only 38 seconds.

Look at the attached image - the Playhead is at 18 seconds, where I wanted the images to be inserted. And the images START at 83 seconds! And the images are 30 seconds long? What is going on here?