Placeholder in dialog inside composite

I've created a composite with a dialog inside the widget, but the configured placeholder is not carried over.

In the designer it works, here you see i'm inside the third composite:

But when klicking the third button in chrome i get the value of the first composite:

I have a snippet that looks like this:

A customer of ours found this and I managed to reproduce it in a small test project that are attatched below.

Designer version 2.15.0 with Server version 2.15.3 (Behaves the same in 2.14 though)