It may seem strange, but it is actually a very natural consequence of the way the PerlMonks database is arranged. You see, the Categorized Questions and Answers are "owned" by QandAEditors, regardless of who actually wrote the text.
Consequently, to show you the Q&A nodes you wrote, the PerlMonks engine has to scan for nodes owned by QandAEditors* but written by you; whereas, to show you all your other nodes, the engine simply scans for nodes owned by you. Written separately, the two queries are simple and fast. If they had to be combined, it would result in an ugly, inefficient mess.
So, in a nutshell, it is done this way because it is better for PerlMonks, even if not better for you. Sorry!
See also: Why is the "number of write-ups" wrong?
* (Having Categorized Questions and Answers "owned" by QandAEditors gives them the editorial control over that section that they really need. See How does editing work in the Q&A section?)