I think I found a bug. When player in Doom receive exactly 1% damage, the screen will not flash red at all, and face on status bar will not change. I checked, and bug is present in vanilla Doom 1.9, ZDoom 2.7.1 and PrBoom+ 220.127.116.11. Is this bug known?
It can easily be demonstrated: start E1M1 on "I'm Too Young To Die" and go to courtyard, then pick blue armor and stand in the nuclear waste pool (it will deal 1% damage to player).
The bug happens because damage is added to varirable "damagecount" (it becomes 1), but then it decreases by 1 and set to 0 the same frame before drawing screen (if (player->damagecount) player->damagecount--;), so both screen palette and status bar face will not react (damagecount is 0 already when screen is drawn).