I've got a problem with a curious bug in Vegas (19.0 Build 424): When applying fx "picture-in-picture" on a png graphics with transparent background in it, there is a thin but visible frame on the edge of the layer (also visible in the exported video).
Post a screen shot:
Tell us about your hardware and drivers.
If I turn off GPU acceleration, the line disappears.
The frame exists not only with png layers but also with normal text layers (when using pic-in-pic fx):
As workaround I do it without picture-in-picture fx but with video event cropping or track animation.
I am having this issue as well and I have the same GPU as you. However, I only notice this issue while using Vegas Image. I haven't noticed any problems in Vegas Pro, but I'll double-check.
My guess is it's an issue with the GPU drivers. I filled out a bug report in the Radeon software, might help if you do the same! Annoying little bug but at least there are workarounds.