A lot of times, a user will run into a miscellaneous change to vanilla behavior, and wonder which mod is causing it. I think it would be nice to have a centralized easy-to-find article that documents these.
A few examples:
Beehives - Forestry
Nyan Cat Splash - Portal Gun Mod (I think)
Floating Islands in 1.1.4+ - Tinker's Construct
Levels and Hunger mostly kept on death - Tinker's Construct
Mobs *spawn* wearing your equipment - Unknown (JadedCat doesn't know about it, so it's none of her mods). Note that often people will notice mobs wearing power armor, nano armor, or quantum armor and think that it's a bug in those mods for not blacklisting their armor, when they actually did, and the player doesn't realize that the mob is wearing the same armor that they or a nearby player are. I discovered it because I always wear assorted armor and found it on a zombie pigman, wielding my fairly unique TiC shovel.
This is especially useful for things you can't simply pick up, read the block name of, and then punch it into the wiki searchbar.