Mapfail can occur because of the following reasons.
*CICS Receive Map did not receive any data from map because
a) User pressed a PA key (e.g. Page Up/Page down) instead of PF keys (F1 --> F12/SHIFT+F1 --> SHIFT+F12)
b) User pressed Clear key (Escape key)
c) User pressed a PF key or Enter key, but none of the lebelled map fields (fieldname+I in assembled map listing) had MDT on
(i.e. FSET not specified for any DFHMDF macro) and map did not have cursor location set (CURSORLOC = YES)
d) a CICS Receive Map was executed without any prior CICS Send Map in application program (note - CICS receive map can only receive
Yes it is true that you would need to set MDT for atleast one input fields ON to avoid MAPFAIL provided user presses a PF key/Enter key.