I had a very similar behaviour about 3 years ago in the LabVIEW 7.x days. I looked at your VI and my old code, and in fact: It is the same in 8.2.1. (I missed in making a note at that time to post it later e.g. to this forum.)
"My way" of avoiding this was: Make the border of the chart transparent.
Minimizing the FP and making it reappear will also result in a correct redraw. (You will surely not like this idea, isn't it?)
Moving another object over the "bad drawings" also helps.
Are there any further ideas?
Guenter