Desecrate Bug???

Went to desecrate an item with only 5 modifiers and when I desecrated the item instead of adding a desecration slot on the item it completely removed and replaced one of the 5 t1 modifiers I had. No I did not have 6 modifiers to begin with there was only 5. Correct me if I'm wrong, but isn't it not supposed to delete a mod when there is an extra slot still left???

Did you use any omens when you desecrated, they can override the filling empty mod and add specific pref/suf. I think even the omens for like kurgal/amanamu etc mods can do it in some cases.