MAC was a Macro assembler for computers of the NORD-1, NORD-10, and ND-100 lines from Norsk Data.
This behavior caused some programmers to adopt the practice of writing only the last five letters of a name in their program code as the assembler would ignore the rest anyway.
Another peculiarity was that the assembler worked by adding together the "values" of all the symbols in an instruction to form the actual machine code.
Another issue for assembler programmers in general is the list of so-called monitor (MON) calls.
In the latter days of SINTRAN the problem then was to find available codes for these system calls as all 256 of them had already been taken by several such near identical functions.