It seems that the checkbox default values are picked up if you use test rather than a boolean.
Within the Form (per)
This does not set the default value:
CHECKBOX d1 = FORMONLY.day1, NOT NULL, TITLE="Monday",
VALUECHECKED="Y", VALUEUNCHECKED="N", DEFAULT="N",
COMMENTS="Allow Ext.Lab";
This does:
CHECKBOX d1 = FORMONLY.day1, NOT NULL, TITLE="Monday",
VALUECHECKED=1, VALUEUNCHECKED=0, DEFAULT=0,
COMMENTS="Allow Ext.Lab";