1. s.: I'll also gladly take suggestions for shorthand to use in the reminder text.

p.s. seriously?
p. s. trying again?
P.S. third try
P. S. and fourth

Not occurring here. Confusion.

1. s.: does this work?
2. 1. : does this work? p.s.: does this work?
3. 1. does this work?

EDIT: a. b. c.? Apparently I stumbled upon the syntax of some sort of list?

Also: capitalization seems to be irrelevant - even replacing 'P' with 'R' made no noticable difference. The periods and spaces seem relevant.

Hah. Yeah, I'm afraid my Markdown library thinks that a paragraph (i.e. after two blank lines, which is why V's example doesn't trip it) which starts with [letter][dot][space] is intended to introduce a list.

V's examples spread into paragraphs demonstrate what's going on:

p.s. seriously?

1. 1. trying again?

P.S. third try

1. 1. and fourth

Workarounds: Remove the space to "p.s.", or remove the dots to "ps:", or insert a backslash \ between the first letter and the dot, so your paragraph starts [letter][backslash][dot][space].

This isn't really a fix, but I basically use "Edit:" or "ETA:" instead of "ps." in comments :)