Can't replace clip

I know I've been able to hover a clip over an existing clip in my timeline and it will turn white and give me options to replace, audition, etc. For some reason it's not doing that anymore and only moving the clips out of the way. It's probably something check or unchecked, but I can't figure it out. Anyone have any ideas?

I think I realized what's going on. I can't do that from the timeline, but when I grab a clip from the event library my existing clip turns white.

That's it, you can't do it from the timeline. You've probably realised by now, selecting the clip in the timeline and hitting ⇧F gets you the range you want to replace in the event.