Version: (using KDE 4.3.1) When in Preview mode Dolphin tries to create previews for all files including folders. While it very ok ;) with folders having default icons, it is pointless for folders, having custom ones. It should either not to create previews for folders with custom icons by default, or separate it as "Folders" And " Folders with custom icons" in "Show previews for..." Dialog. Thanks
*** This bug has been marked as a duplicate of bug 201850 ***