Fix Positioned#cloneIn

[mbovel]

Fixes #13626.

[smarter]

LGTM, but could you squash the two commits together? Having the functional changes and the tests in the same commit makes it easier to tell what a change is for when stumbling upon it via git blame for example.

[smarter]

One more nitpick: descriptive commit messages are nicer, so consider using a commit title like "Fix Positioned#cloneIn to also update the source" instead of "Fix #13626" (and move the "fix #..." in the commit message body), I think you said this fixes a regression, so you could also mention the commit where the regression was introduced in your commit message.