This seems worst than I realized... a bug? I thought you (Djorgje) had a good idea, so I tried it today getting a plan ready to send off, and I can't open them either... except for 3 of 46 stairs. All the stairs (except the 3 that opened) have the same modification date of March 25, 2003. I wonder if that date corresponds to an AC update. The 3 that open were created later than this. Interestedly the 3 that opened (and I did not modify them or re-saved them) now have todays date as the modification date. Their creation date is after the modification date that shows up on the ones that want open. This is not great news for me since I deal with the same plans over and over and the stairs are not obsolete.
Thanks for the suggestion, but something else is going on.
If someone else would check their old stairs and see if you can edit them, I would appreciate it... especially Mac users.