"Uncommitted changes" when there's nothing to commit with submodules

I have a Git repo with a submodule that has uncommitted changes. The Log / History view shows "Uncommitted changes" on top of the graph (see attached screenshot). However, the parent repository doesn't have anything to commit, so the "File Status" view doesn't allow a commit to be created ("Nothing to commit" is shown and the "Commit" buttton is greyed out).

In SourceTree 1.7.0.352509, the behavior is far less confusing. It shows a "..." in the list of submodules on the left, but the Log / History view doesn't claim that there are "uncommitted changes".