Equation & R-Square Value of Trendline Remained Unchanged

I just realised that the equation and R-square value of trendline on my scattered plot remained unchanged when I modified its data.

So what happened was:
1. The plot (scattered plot, with power trendline, equation & R-square) was originally created in a spreadsheet (Sheet 1).
2. A copy of Sheet 1 in the same book was then created (Sheet 2).
3. The data in Sheet 2 were modified. The data points on the plot moved BUT the equation and R-square value remained unchanged.

And what I did was:
1. Deleted the trendline, equation and R-2 and reconstructed them. Results: They were still the same.
2. Deleted the data points and replotted the graph. After that, trendline, equation and R-2 were created. Results: The equation and R-2 magically changed!

Anyone can explain this?