All the latest versions - right now Maxwell Beta (22.214.171.124) SolidWorks 2015. I have had it for years - always. I know how to solve it - checking and unchecking again makes it "unlocked" for OBJ export.
Thanks, but I'm still not able to observe this, neither when creating & exporting a part (e.g. a simple box) from scratch, nor when opening a previously-created SW file. Please let me know if you can think of any other factors that may help me to reproduce it here.