softmax activation in GRU

Hi, I noticed that you put softmax activation inside GRU cell, as I understand in this case you wont get sum of activations for each timestep equals to 1. Here is link for GRU cell and the same situation for terminal GRU https://github.com/HIPS/molecule-autoencoder/blob/master/autoencoder/train_autoencoder.py#L225

I also checked with you version of keras that it does not sum to 1, here is link to ghist https://gist.github.com/fgvbrt/1f2e1828c6d8c0eb88614f14c60874ad

Was it done on purpose or was it mistake?
Thanks in advance.