SharedStringTable calls split_string_setup which isn't accessible from its context. Big enough block_length is needed to trigger the bug.
Please find quick fix with test case in my branch. I was considering an alternative change, which is pulling split_string_setup out of workbook.rb into helper.rb, but diverged from that. Wanted to keep global namespace from extra pollution.
Let me know if changes make sense.
trying out quick fix for MethodMissing split_string_setup
test case that triggers hardcore SharedStringTable block sizes calcul…
yes, it's bug. I've merged your patch and released new gem.