Hi Nick,
very good observation. Just wonder are we the first who observe this problem?!
It seems org-table-make-reference and calc-eval have some sort of an different idea of the data content.
Yes calc use that notation to deal with imaginary numbers. Funny coincidence, the students in that list just struggle with exactly those imaginary numbers and now there names became a imaginary number itself... ;)
Thanks for the tip, I will see if some search and replace helps me to create a intermediate solution.