Gmaps4rails doesn't display my marker until re

Question

I implemented a Gmaps4Rails Map in my app:

Link to one Location, you may go back to the list with the link at the bottom and check another location ---http://immosmap.herokuapp.com/locations/37

My problem ist that I get this error and it only displays a blue map:

Uncaught TypeError: Object # has no method 'setMap'

But when I reload, it does display the way I want it to work.

Do I have to implement a callback here? How? Didn't find my topic in the wiki...