It happened since V13 (now using V15) when I had this problem of unable to delete Predefined Zoom after saved and named it. The list gets longer and problematic as I saved more zooms. The saved zoom can be deleted during the same session though, after that they would get greyed out when reopen again.
Running Mac OS 10.7.1 with Mac Book Pro 2.4 GHz Intel core 2 Duo, 4 GB 667 MHz DDR2 SDRAM.
I have the same problem since AC13. I use a highly modified Master Template and it is impossible to clean it up. I think it is a very serious bug especially if you want to implement "visual legends" as described by Eric Bobrow.
I just made a little experiment with AC14 v4044. I made a new file from the default international template and the predefined zooms worked as expected. I can delete rename etc.
So I think the problem must be in the pln database itself. The Master Template had the problem from the beginning (I think I got it from v13) and it remained from version to version as I make my own updates and customizations and localization. I can ask permission from Eric Bobrow and send Graphisoft a copy for further examination. I would like to clean my template without making everything from the beginning, if this is solvable somehow.
I made a further test and I reproduced the bug. You have to save a predefined zoom and then change the window size. Choose the zoom from the list and the view changes as expected but you do not see the little tick next to the zoom name and you can not delete, rename etc. And now the best part: Resize the window to the previous size and voila everything works as expected.
So it is a very serious bug for us osx users with the all around floating windows. It is a lucky guess to reproduce the window size of an other screen resolution or even in the same screen if you saved a zoom using a custom pallette / window layout.