Similar thing happens when removing a mod. When installing an additional mod X, it is quite easy to overlook a patch between X and any of existing mods, unless it is provided on X's mod page. Unfortunately, when editing an existing mod list, it doesn't work because most patches are provided from only one of the mod pages. If I target a perfectly pre-arranged mod list (such as STEP) and install them one-by-one from the beginning, it is possible to grab all of those patches by carefully navigating each of mod pages. Now let's get to the modder's perspective. To handle those side effects, lots of them are providing compatibility patches for other common mods. In Skyrim, there are lots of mods that influence other mods' functionality.