I've searched for hours now and still have no answer to this problem.

You can right click on a custom pivot table style and select, 'Modify', 'Duplicate' and 'Delete'. I have no pivot tables using the particular cusom style. Selecting 'Modify' does nothing and doesn't invoke the create custom style window to allow for editing. Delete shows a pop up window asking if you want to delete the style, selecting 'Yes' does not delete the custom style and 'Duplciate' works. The problem as many people have pointed out is that you can't view your custom style until you click ok, but if you want to tweak it further you can't, you end up having to create another custome style from scratch which is a complete pain because you end up with loads of custom styles you don't want, can't delete and can't edit.

Is this a known bug or is there any way around this problem.

Many thanks