REW 5.31.3 RT60 avg/export

I just took about 20 measurements all over the auditorium I'm trying to analyze. I can average SPL, but there doesn't seem to be an average for RT60. I get the concept might be tricky to "average" but I'm trying to piece together a treatment plan. I did find an announcement that this feature was added in REW 5.20.14 but it seems to be missing in 5.31.3 (at least in the Linux build). Disappointing but I figured I could still export them all and average it in OpenOffice, except that "Export RT60 data for all measurements as text" happily does only the last (or perhaps current) measurement. I was really hoping not to have to save them all individually and merge them - am I doing something wrong or did I find a bug?

Use the RT60 overlay graph in the Overlays window, the option to show the average is in the graph controls, it can be exported from the graph actions.