I have a kegged batch of beer (Munich lager) that was quite sweet prior to fully carbonating. After carbonating there's a significant bitterness - not a hop bitterness (there is little in this batch), but a plain lacklustre bitter/salty - middle-back of the tongue.
I've noticed similar things in previous batches which makes me wonder if this is the CO2 and carbonic acid at work. When I decant the beer several times to reduce the carbonation, the bitterness is greatly reduced and the malt/sweetness returns.
To be sure, I should probably do an experiment and measure temperature after decanting since that also affects taste, but is it normal to adjust a recipe to account for carbonation?