Muon Analysis sequential fit doesn't use period selection

Expected behavior

Sequential Fit should use the same period (or period combination) as selected in the Home tab, plotted in the graph, and used for individual fits.

Actual behaviour

The result of the sequential fit is the fit to period 1 regardless of the user’s choice.

Steps to reproduce the behaviour

Load a multiple period file (first of several such runs). Select period 1 to plot.
Fit it to a function.
Do Sequential fit to the set of runs.
Go back to Home and change the period to 2. Re-fit, observe parameters change.
Re-run the sequential fit (with a new label).
Generate the Result tables of the two sequential fits and notice the suspicious similarity.

Platforms affected

Mantid 3.9, “Classic” version of the Muon Interface fitting dialog. Seen on Windows, maybe others.