Truly bizarre - adding legend breaks custom sort on X axis

Hello, 

Thanks for the suggestion, but no - that's not it. The week number is already formatted as a number. I tried to switchong to text, to see if that made a difference, but it didn't. It still lists all the week numbers if there is a value for the first variable of the legend, then moves any numbers where there is no value to the end of the scale, ordered according to whether there are values for subsequent variables in the legend. It's absolutely bonkers.