There are 2 different settings of “level” for each item. One is named “Stats - Level” and the other is named “Stats - Level (Unclassified)”. For most items these 2 settings in object editor in items tab are different, for instance “Legion Doom-Horn” has level 5 and 7. Please completely delete the setting “Stats - Level (Unclassified)” and make Warcraft 3 and the World Editor use only “Stats - Level” for browsing, creating and dropping items (GUI, Tool Palette, Triggers, Units Properties…).
I made a complete list of issues with items here: Items that need to be updated or terminated