If I drag, say a photo onto the timeline, I get a red box until I release the mouse, then the photo is added, and box disappears.

If I repeat with an XVid clip, the clip is not added, but the red box remains. If I repeat, then the red box then gets removed.!

I can keep repeating to make box stay/hide as I wish.

Not intending to use the Xvid as real footage, but it was handy to try something, and instead noticed this.