There might be a pattern that the entered category is one that mouse pointer hovered a little while ago. If clicking repeatedly on Development and being careful not to hover over any other categories, Development is always entered. Tested about a dozen times.
I also cannot reproduce this if I select categories using keyboard and keep the mouse pointer always on top of the button to go back to All applications.
Steps to Reproduce:
1. Open Kickoff
2. Switch to Applications tab
3. Click on Utilities
4. Click on All applications to go back to category selection
5. Click on Utilities again and repeat 3-5 if necessary
Sooner or later some other category like Development or System is entered even though Utilities was clicked.
Clicking on Utilities enters the same category.
*** This bug has been marked as a duplicate of bug 332808 ***
Fixed with ad0c73b3 in plasma-desktop
Note that this is was not fixed with that commit, I can still reproduce this.