Well, at least I know I'm definitely not alone in this. Confirmed that it's happening on the demonstration site Orion has set up for us... 8-)
I did also notice one other thing, the lower the volume your interface is, the closer the percentages are to being correct. With very low volume interfaces its pretty much right on...
What you're seeing is that the pie chart is calculating % based on relative percentages (i.e., if you are set at Top 10, it will calculate % based on those 10, but if you set it at Top 20, it will calculate % based on the top 20) and the table is calculating based on absolute percentages (i.e., it calculates based on Top 100, regardless of how many items in Top XX).
So this is a bug, and we are working on a fix.
In the meantime, you can get the numbers to match if you go to NetFlow Settings > Global Settings and set everything to Relative Percentages. The table values and pie chart values might be off by a percentage point, but they're basically the same.