Dependency interface change not detected.

I have two modules: Main and Library. Library is a dependency of Main. Library has two data definitions: A and B, which are co-dependent. Main calls a value called info of type A, declared in Library, and prints it.

main.hs:

module Main where
import Library

main = putStrLn $ show info

library.hs:

module Library where

data A = ARecu B | ABase String deriving (Show)
data B = BRecu A | BBase Int deriving (Show)

info :: B
info = BBase 1

I compile with the command ghc -o main library.hs main.hs and then run ./main. Everything works fine. The problem is when I rewrite info to a value of type B, as follows:

main.hs:

module Main where
import Library

main = putStrLn $ show info

library.hs:

module Library where

data A = ARecu B | ABase String deriving (Show)
data B = BRecu A | BBase Int deriving (Show)

info :: A
info = ABase "Hello"

After recompiling with ghc -o main library.hs main.hs, and then running ./main, trash is printed, or a segfault happens, basically just undefined behavior.

Observations

When I recompile, only Library is recompiled, not Main. This doesn't make sense. Since the interface of a dependency of Main changed, it should also recompile. I suspect something's wrong with ghc's dependency manager, since it should infer Main has to be recompiled.

Since Main isn't recompiled, it's trying to call a Show instance of type A over a type B. This causes the undefined behavior.

Weirdly enough, this bug only happens when I use co-dependent data, like A and B. If I take that away, say:

data A = ARecu B | ABase String deriving (Show)
data B = BBase Int deriving (Show)

recompilation now works fine. Main is recompiled, and everything runs as it should. Maybe the bug is somewhere near there.