You cannot bound political parties to follow certainly defined political agenda. If majority of Pakistanis voted for secular agenda of Awami League, as per peoples wishes, Pakistan should have been changed from Islamic to secular republic. Constitution of Pakistan can be changed in any form after getting 2/3 majority for a certain clause. There is no authority to overrule that much majority in any democracy.The first condition in the Legal Framework Order 1970 was that Pakistan would be based on Islamic ideology. Talking against that or preaching regional hatred was outlawed in the martial law regulations and Awami League did both.
And yes the Constitution of Pakistan which all political parties are signatory to encloses the Islamic ideology. It is also a crime in our penal laws to talk against it today.