I recently noticed that my slowed down footage doesn't show at its true length when conformed within Vegas 15 Pro (261).
Example: I use Sony cams and import 60, 120 and 240fps footage into Vegas onto a 24p timeline.

When you hit confirm to project frame rate, Vegas 15 (261) keeps the slowed down file length the same as the original footage, meaning most of your slow motion is not displayed. Going from 120fps to 24fps should be 5x longer on the timeline (though Vegas is limited to 4x for some reason- .25x is its minimum).
So if you manually drag the clip 4 times longer you can see all of your footage.

Now changing the playback rate manually also doesn't show the rest of the clip. Nick confirmed this has been the behavior since at least v10 in Vegas, so perhaps it's not a bug but was an unfortunate surprise for me.

I wish there were a checkbox to "match clip duration to playback speed" , the right side of the clip flashing red at first or something like that to make it explicit there is more footage!