I can confirm this behavior, but Iím not sure itís unintentional on PyMOLís part. Rather, I think it may have something to do with two facts: 1) unlike loops, sheets represented in automatic mode are not radially symmetric; and 2) unlike helices, the orientation
of the sheet at a particular CA atom cannot be determined by its immediate neighbors. I havenít had a chance to look at the relevant source, so I canít confirm this at the moment, but it seems likely to me that PyMOL uses the other (non-CA) backbone atoms
to define the ďflatĒ plane of a sheet, and without this information, instead of guessing at its orientation, it omits the sheet entirely. (This also appears to be the case for other non-radially symmetric modes, including dumbbell, rectangle, and oval.)
Could you get by using different colors to indicate your SS assignments in another cartoon mode?