(This is similar to #25026 but I think the problem is somewhat different - however, it might be seen as a duplicate of that bug. I don't mark this as RFE as I consider this a (minor) bug. Your mileage may vary ...) When first logging into KDE, the icons are arranged horizontally. After doing an "arrange icons" they are arranged vertically, as usual. Should IMO always be arranged vertically.
This defect is considered MUST-FIX for Florence Release-Candidate #2
This isn't a bug, it's a preference (I too would prefer vertical alignment, but that doesn't make it a bug).
*** This bug has been marked as a duplicate of 25026 ***