You see all sorts of playback anomalies on HD TV with non HD content. The industry does a poor job explaining this.
I take it that you did use another VCR since you claim it's not the problem.
I recently bought an LG HD Tv that I also use as my computer monitor. All's fine except when I playback a VHS videotape the monitor skakes a bit.I never have this problem with my old regular hitachi TV. Not the VCR causing the problem.