When you say it “shifts”, do you mean it does or doesn’t respect the new margins if, after a page deletion, it moves from a right page to a left, or v.v.?
I just tried a test document (CS6), using different inside (15mm) and outside (9mm) margins, 5 pages, laid out in spreads (1, 2-3, 4-5).
I put text boxes in 5 positions on page 3 as follows:
a. touching both left and right margins (i.e. the usable width of the page);
b. touching only the left margin;
c. touching only the right margin;
d. left of centre, with left edge aligned to right edge of box (b);
e. right of centre, with right edge aligned to left edge of box (c).
Then I deleted page 2. The old page 3 became the new page 2. It contained all the elements from the old page 3, aligned just as described above. i.e. I didn’t need to manually shift any text boxes, as they stayed in position relative to the margins and relative to each other.
I don’t *think* primary text frames have anything to do with it.
Chris.