A couple questions before I can answer your concerns.

Are you reusing the same charLSTM in both places?
The Is charLSTM an RNN class or an RNNCell class?
The torch.cat( [ word_embeddings[i,:,:], char_rep[i,:,:] ] ) call will concat along dim 0. Depending on the class of your charLSTM, this has different effects. Are you sure that this is what you want?