Only today, when playing Hacx I noticed a suspicious loss of health when tracking down the robots from below. Then I tested it with Doom. Indeed, firing a rocket straight (90 degree up) up will kill You/seriously damage You, no matter how far below of a high ceiling You are.
I redownloaded the latest 9.0.12 version.
The damn things still kill You, so I suppose it's time to report this well.. discovery.
EDIT: Also: I just love bugs that come out in development

EDIT:
I've taken my research on this further to report that the rockets aren't the end of this weirdness. All splash-damage weapons make this happen (tested with the Weaopns Resource Wad), damaing You about 4*the splash damage of the weapon (uncertain of the value here..)
The only exception is the Phoenix Rod of Heretic which appears to hurt You only at certain angles.. speaking of Heretic, try firing mace's explosive balls straight up or down. What You'll get, will be quite bizarre.
*I took a screenshot of balls fired up bouncing lightly to infinity and balls fired down bouncing ultra-fast.. infintely, but the screenshot refuses to show the hi-speed balls*
My question-what the heck is going on?