Hi,
Are the calls being answered on the headset or on another phone (twinning, softphone)? For the Call History softkey to light up you must miss the call on the headset itself, otherwise, if the call is answered (from it), it shouldn't light up.
I run MiVB 7.2 with 5330e phones, and I've tested this over and over and can't replicate unless I answer from my cell phone or MiCollab.
Can you confirm with further details that this is your case?