Why can I modify partitions on a device with an amiga or bsd partition table?
KDE Partition Manager currently only allows read-only access to any other partition table type than MS-DOS. This is for safety reasons: Support in KDE Partition Manager for this partition table types is not really there and what is there (or just incidentally works) has not been tested enough to use it with confidence. Of course you can still create a new MS-DOS partition table on the device in question, but that is probably not what you want.