Note: As you found out yourself the only exception to the "UT doorbombs are as dangerous as a kobold" statement is that explosions, even really weak ones, can break stuff. If you're holding a mine or attack wand (striking, fireball, lightning) and it breaks, you're going to feel a lot of pain if not wind up dead. Even if you're not, you may want to put breakables like wands or bottles away (either on the ground or in a chest) before kicking down doors. Generally though I don't find myself with many wands/bottles of healing/troll blood before the UT is done, so I feel free to kick down locked doors.