Text scrambled with fo=aqn, numbered list within comment

[photm5]

If you set fo=aqn, typing text at the end of a line can scramble the text –
i.e. after typing one character, the cursor is misplaced so that the next
character ends up at the wrong place. To trigger this, place a numbered list
item within a comment:

1. Run vim --clean
2. Type i* f<cr>* 1. foo123456789<esc>:set tw=17 fo=aqn<cr>a weird
3. The word "weird" is broken up into its individual letters, and they are
   inserted in inverse order with spaces in between: d r i e w

I expected it to insert weird on the next line (plus the comment character and
indentation).

The setup looks like this:

* f
* 1. foo123456789

The result looks like this:

* f
* 1. foo123456789
*    d  r  i  e w

The result should look like this:

* f
* 1. foo123456789
*    weird

I reproduced the bug on the following machines:

• Vim 8.2.735, i686, void-linux, rxvt-unicode-256color
• Vim 8.0.1453, x86_64, Ubuntu 18.04.4 LTS, rxvt-unicode-256color via ssh