LTE to 3G when in call or voicemail ????

Haven't seen this discussed here before (maybe I missed it), I don't really know if this has been ongoing or just started during a recent update or not, but I just noticed that whenever I make or am in a call, or dial my voicemail, the signal indicator always goes from strong LTE to H (3G?). Is this normal? Anyone else see this?

Thanks, just curious.