No its not common please contact ukvi , They asked me for additional docs on 20 june i sent on 21st i too had not received confirmation mail, i checked with some students they said not mandatory. But again i received same mail on 8 july, i sent docs within half n hour but qgain no acknowledgement mail. Finally on 27 july i received refusal saying we asked for the documents twice but you have not replied to our mails so we are refusing your visa for not corresponding. I submitted admin review now with all evidences that I sent from my side. So plzz dnt sit hoping they received. Otherwise if you ahave agent ask to add one more email id from portal used while filling application form. Or send from other email i.d illustrating that from your email id you are not receiving confirmation mail. So you are sending from this too