By default Dolphin shows system partitions like root and home under External Devices in Places Panel. These should be hidden because are redundant, maningless and simply should not be shown to normal user. Reproducible: Always
Most normal users aren't going to have separate /home partitions. Also, the label is "Devices", not "External Devices", so hopefully that reduces confusion a bit. The problem is that there are an awful lot of people who really like using Dolphin for volume access and management, and this change would upset them. I don't think there's anything we can do here for now.