R plot(surv(), newdata=...) draws same lines many times - why?
Note that in the linked presentation, on the slide titled "Plotting the effects", the treat object has only 2 rows.  

In your case, because frame has 57k rows, fitObjGrouped has predictions for each row of newdata.  You can verify this with fitObjGrouped$n.  To fix the problem, try:

frame &lt;- data.frame(group = unique(dataset$group))