Opps, I am on 10.9.4 I just forgot to update my profile. So it is not an OS version issue. However, for kicks this morning, I opened a fresh file with a default AC 18 template (Residential) and had no issue at all. I went back into the former file which is an new AC 18 project but uses a highly customized WE and company template, thinking that some setting must be creating the problem, but it worked fine there too. A strange problem since it definitely did not work correctly the other day.
Don, I too have been very slow to update to the new OS, in fact I just did it last week. So far there haven't been any issues.
Erich
AC 19 6006 & AC 20
Mac OS 10.11.5
15" Retina MacBook Pro 2.6
27" iMac Retina 5K