hptSomeThingsBelowUs missing module

Ever since upgrading to 6.12.1, I've been getting a new warning. I compile with --make, e.g. (clipping out irrelevant stuff): ghc-6.12.1 -threaded -W -debug -package ghc --make \ -main-is App.Main App/Main.hs \ -o build/seq If I remove all imports to a module (say Util.Debug), compiling other modules prints this warning: WARNING in hptSomeThingsBelowUs missing module Util.Debug Probable cause: out-of-date interface files I searched on trac but didn't see anything with this name. Is this a known issue? It doesn't seem to cause any harm in the eventual binary, but is somewhat alarming to see a bunch of them scroll past. Manually wiping out a bunch of .hi files causes recompilation and the warning goes away.