Sorry for the late response! The reason the dialog box leads to the research instead of engineering is because the previous research just finished and as such there is no active research selected right now. It honestly is quite confusing at times and I suspect there's a few bugs with the pop-ups, but the gist of it is: Research finishes -> Assign research project on the dialog box, engineering project finishes -> engineering project button on the dialog box.
If you've noticed that there are projects that don't follow this logic, and I think there might be some, that is a bug. If you don't mind, please let us know! Thanks very much!