Question to people known to sony vegas

[Bakpao]

Does anyone know wtf these little triangular holes are?
Most of the time they're not harmful at all and that's why i thought they had no meaning but more and more often soon they tend to mess up (fragments of) my videos. It's easy to fix, but it takes time to do it..
Idk wtf they are XD

If pic is too small to see click this CLICKCLICK

[BlacPlague]

nvr knew they did anything, i though they were just spacers in the clips

[Bakpao]

thats what i thought but apparently they have meaning in my sony vegas -______-
They also just appear at random (well thats what it seems like to me but they probably arent)

[Achaeon]

if what I see is correct then you can drag it backwards then it will fade slowly out
if its not that then idk XD

[Bakpao]

Tried dragging them ended up lowering the opacity of the clip so that's not it lol.
I think it has something to do with transitions but meh I have no idea what xd