-I= flag appears to not work the same way it did

[fieldvoid]

I have an old project that I believe I normally compiled with dmd -i -I=./source/ app.d because that's what I have in my makefile. It currently errors and the workaround is to write dmd -i -I=./source/ source/app.
It is possible that passing app.d that way was never supposed to work and that telling the compiler exactly where it is located is the intended behavior, but in case this is a bug, I am opening this as an issue.