My thoughts on moving and attacking are as follows:
A Large Monster (LM) begins its Move Action with Overlord (OL) indicating his/her selected 1x1 "shrink" space. The LM then moves any amount less than its max movement points and OL declares an Attack Action.
The hero may interrupt his movement with another action and then complete his movement after the other action is resolved. p7, "Move"
Declaring this puts interrupts and puts aside the Move Action, retaining its 1x1 shrink space and the action is effectively phased out. The Attack Action continues until it is complete.
At this time, the Attack Action is no longer happening, and the Move Action is then resumed. I think it is important to note that a new Move Action is not starting, it is merely resuming the pre-Attack Action move. Therefore, a new 1x1 shrink space is NOT chosen since it was decided upon during the initial move. As indicated by the text below: I believe the word "movement" is singular and is equivalent or synonymous to "(a) move action"
When determining movement for large monsters, the overlord player chooses one of the spaces that the monster occupies and counts movement from the chosen space as if the figure occupied one space. When the monster ends (or interrupts) its movement, the overlord player places the large monster figure so that one of the spaces its base occupies includes the space where the monster ended its movement. p16, "Large Monsters"
If the above is true then for a 2x2 LM:
(a) a LM gains 0 net movement points due to an attack action
(b) an OL may declare a move action, end it, change orientation, declare a second move action with a new 1x1 shrink space and repeat
© Dash is a single move action and not 2 separate move actions so the LM may not change orientation half way through
A more sequential diagram explaining is below:
-> Move Action begins, declared 1x1 shrink space
---> Attack Action begins
<--- Attack Action ends
-> Move Action resumes with 1x1 original 1x1 shrink space
<- Move Action ends