What are this lines?

[Caple]

I'm capturing a 1995 VHS, not homemade (but the problem occurs on homemade tapes too), and I'm having this problem on some frames.
Like this

Then, on the next frame

And it keeps like this. Sometimes two frames in a row have this problem, sometimes more, it's not a fixed number of frames.
I'm using a Hauppauge PVR 500 and WinTV to capture.
I believe the problem is my VCR heads, as I use the VCR as a tunner too but I don't have this problem when capturing TV footage.
Any idea?

[Krispy Kritter]

I would expect it to be the VCR, heads or playback circuitry. You could try a different VCR just to verify the cause.

[SLK001]

It's either the original tape or your recording setup. If was the head, the issues would be left to right.

It might be a telecining artifact, but there isn't enough detail to make this determination, and they also generally run left to right (not upper-right to lower-left). Load the video up using VirtualDub and step through the areas where this occurs. Tell us what the results are.