Those who set MDA in the MCP window take care.
I am not a Boeing driver but I am familiar with some of their operational recommendations and those given for other highly automated aircraft. On some aircraft the reason for selecting MDA in the MCP window is to enable the selection of vertical speed for descent on the final approach. (For those flight guidance systems requiring Alt Sel change before leaving an altitude.) After commencing the final approach many manufactures recommend that the missed approach altitude is set in the MCP. This avoids an unnecessary level off at MDA (which may encourage bad practice or destabilises the approach) and, with some systems could prevent false or misleading altitude capture during go around from below MDA. If a circling approach is planned then the circling altitude may be set.
Thus do not leave MDA in the MCP; if you require a MDA reminder use the DH bug, grease pencil (non EFIS), and even ‘the non flying pilot’!
If in doubt follow the manufactures procedures, they have been thought through against a background of deep system knowledge and in the fullness of time with the many experiences of many operators.