Blizz raid frame showed same as grid, otherwise I wouldn't post it as a bug
Edit: As you can see from the screen shot here, Blizz UI and Grid agrees on what people are in what groups and such, while the nUI frames shows wrong number of people for the various groups (ie. nUI shows three people for G1 and G2, Blizz and Grid shows two for G1 and four for G2)
On my dps alts this is no issue, but on my resto druid main, this is a bit of an issue. When we raid we usually have 3-7 people on standby. It's not good to have those people show up among the 25 people actually in the raid. Hence the need for grid (has always been like this for me using nUI. The raidsort feature has never worked for me).
Edit2: In the 2nd screen shot, you can see my group ID as 4 in nUI, yet I am clearly in G2.