Factorio Forums

Perhaps not a "bug" per se, but the mod database seems to allow you to install mods you already have, if you have an older version of that mod, leading to a crash on load with an error "Duplicate mod [Mod Name]". Were I not used to installing and updating mods manually (i.e. were I not to know in which folder to find my mods) I would likely be lost, as the error does not tell the mod folder.

This seems to be an oversight, as the game does not let you install mods you already have installed if they are the same version.