I would presume it is the sed line added in commit f09030b but that works on all the systems I've seen it run on so I can't really tell why it causes a problem for you.
I have tried the sed command from that commit, with no trouble. The issue is that the command is being executed inside a sub-shell, so ksh needs a double escape for ", as in \\". Instead of sed s/\"//g, could you use a more stable sed 's/"//g' instead? I can provide the simple Pull Request, if desired.