Modulate Vector block and double filtration

Hello Community,

Recently I investigated Modulate Vector block and my observations are that this block has two filtering stages - firstly in the modulator (RRC filter) and secondly in itself (user providing the filter taps). The simple scheme of operation looks like in the below picture.

So the question is: what is the purpose of the filter in modulate_vector_bc function?

Is this a bug or is there a reason for this? 

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BR,  

Marcin Puchlik