Many thanks for pointing out the rotate tool. Initially I had been typing the rotation value directly in the object info palette, as this is what I had been doing in 11.5 with no problem. I tried the rotate command and it was behaving the same as typing the value into the object info palette. I had not tried the rotate tool so at your suggestion I tried it and it works perfectly, many thanks!
In case anyone is interested, after more experimentation here is what I've found: The rotate TOOL always works properly (i.e. the scroller stays at the front of the lamp), either selecting the instrument and accessories or just the instrument. Typing the rotation value into the OIP does not work properly after the instrument has first been placed on the plot, but works properly after the instrument has been successfully rotated using either the rotate TOOL or rotate COMMAND, or after the instrument has been moved. These results are consistent for me whether or not the instrument has a position and unit number or not, and whether the unit has a label legend or not. Refresh instruments doesn't seem to affect things at all. The rotate COMMAND sometimes works properly after the instrument has first been placed, sometimes not. It always works properly after a successful rotation using the rotate TOOL.
I spoke with another vw2008 user this morning who was not able to duplicate my problem on his system, so perhaps this is a problem with my installation. He has windows and I have mac, though.