git submodule woe

Problem:
A submodule is stuck in a commit, like so:

$ git show
.................................... shows a stuck submodule
--- a/badsub
+++ b/badsub
@@ -1 +1 @@
-Subproject commit 4ba912892c1b8c213c6c2e78b3bf257635dc534e
+Subproject commit 4b813c322ebe236cddc6b3acd70a31994efd7a56

Solution:
Focus on the commit, not submodule. Submodules work as designed, it's the commit that needs to be fixed (with `git commit --amend`, obviously):

$ cd badsub
$ git checkout 4ba912892c1b8c213c6c2e78b3bf257635dc534e
$ cd ..
$ git add badsub
$ git commit --amend

Nowhere as bad as copying a file while preserving history. Still, not obvious if one focuses on `git submodule`.