Insert-mode gqip not idempotent?

Question

I open Vim and add the following lines to a buffer (call this state INITIAL):

xx xx xxx xx xxxx xx xxxxx xxxxxxxx xxxxx xxxxxxxxxxx x xxxxx xxx xxxx xxx x
xx xxxxxx xxx xxxxxxx xxxxxx xx x xxx xx xxx xxxxxx xx xxxxxx xx xxx xxx xx
xx xxxxx xxxxxxx xxxxxxxxx xxxxxxxxx xx xxx xxxxx xxxx xx xx xxxx xxxx xxx xx
xx xxxx xx x xxxxxxxx xxxxxxxx xx xx xxxx x xxxxxxx xxx xxx xxx xxx xxx xxx xxx
xx xxx xxx xxx xxx xxxx

I then go to the end of the buffer and enter insert mode (GA). I then type <C-O>gqip. The buffer changes to (call this state A):

xx xx xxx xx xxxx xx xxxxx xxxxxxxx xxxxx xxxxxxxxxxx x xxxxx xxx xxxx xxx x xx
xxxxxx xxx xxxxxxx xxxxxx xx x xxx xx xxx xxxxxx xx xxxxxx xx xxx xxx xx xx
xxxxx xxxxxxx xxxxxxxxx xxxxxxxxx xx xxx xxxxx xxxx xx xx xxxx xxxx xxx xx xx
xxxx xx x xxxxxxxx xxxxxxxx xx xx xxxx x xxxxxxx xxx xxx xxx xxx xxx xxx xxx xx
xxx xxx xxx xxx xxxx

Still in insert mode, I type <C-O>gqip again. The buffer changes to (call this state B):

xx xx xxx xx xxxx xx xxxxx xxxxxxxx xxxxx xxxxxxxxxxx x xxxxx xxx xxxx xxx x xx
xxxxxx xxx xxxxxxx xxxxxx xx x xxx xx xxx xxxxxx xx xxxxxx xx xxx xxx xx xx
xxxxx xxxxxxx xxxxxxxxx xxxxxxxxx xx xxx xxxxx xxxx xx xx xxxx xxxx xxx xx xx
xxxx xx x xxxxxxxx xxxxxxxx xx xx xxxx x xxxxxxx xxx xxx xxx xxx xxx xxx xxx
xx xxx xxx xxx xxx xxxx

Still in insert mode, I type <C-O>gqip again. The buffer changes back to A. It may be hard to tell, but A and B are actually distinct. Still in insert mode, if I keep typing <C-O>gqip, the buffer state keeps toggling between A and B. The state progression is therefore INITIAL → A → B → A → B → A → B → ... .

When I try the above in normal mode, the state progression is INITIAL → A → A → A → A → ... (which is what I would expect).

(All of the above works if I use gwip, gqap, gwap in place of gqip.)

I'm not sure if this is a bug or if there's some odd subtlety to Vim's commands that I've never noticed before. I thought gqip was supposed to be idempotent no matter what mode I ran it from.

My question is: What is going on here?

(If you're wondering why all the text is xs, it's because I first noticed this behavior while working on some confidential code, and then replaced everything with xs so I could ask this question publicly.)