Hello, I am writing to report a bug in Athena running on OSX 10.10.4. Here are the steps to reproduce the problem. I'm not sure that all steps are necessary. 1. Open Athena and import the attached project, which contains two groups that are both marked. 2. Change plot range to plot from -30 to 30 eV. 3. Select the "deglitch and truncate" window. 4. Select group "Ref data.merge". 5. In deglitch many points, set margin to 0.05, Emin to -24, and Emax to -20. 6. Click replot margins. 7. Click remove points. 8. Click return to main window. 9. Click the derivative check box to plot marked groups as normalized derivative. 10. Click mu(E) button to plot marked groups as derivative of mu(E). When the last step is done the groups appear to shift with respect to each other. One can switch between Normalized and mu(E) and see the shift come and go. Thank you, George