Torch and shield usage inconsistent with original game
1. I can be wrong, but in my testing NPC hide torches during rainy weather in original game.
OpenMW does not have this behaviour - we check only for darkness (isDark() function).
2. Shield, torch and two-handed weapon equipping is inconsistent too.
In original game, when you equip shield or torch, an engine force you to unequp two-handed weapons.
When you equip two-handed weapons, an engine forces you to unequip torch, but not shield (IIRC, MCP fixes shield bug-feature).
In OpenMW, an engine allows you to equip light sources and shields with two-handed weapons.
From the other hand, we have a hack in Actors::updateEquippedLight() to emulate vanilla behaviour for NPCs, but it does not well: during combat NPC will have both weapon and torch equipped, so the torch will be visible during weapon unequipping animation (another difference from Morrowind).
The simpliest way to fix 2. is to make equipping differences togglable at least.
#1 Updated by Dark Locq about 2 months ago
No idea about # 1, since I don't use MS Windows.
Keeping a shield equipped when you have a two-hander is arguably not actually a bug and should not be changed; it's just strapped to your back or something, and you still get any CE enchantment benefit from it; you just shouldn't be ale to use it for blocking when holding a two-hander. However, you do only have two hands, so of course using a torch and wielding a two-hander are not something you can do simultaneously. It's not OpenMW's role to "enforce" subjective decisions by MCP or any other code-patching project about what people at those projects thought would be "better", even if we do eventually want to address things they fixed which are unmistakably, objectively bugs.
The best behavior from a UX perspective would be to remember what you had equipped, and put the torch away and switch to that weapon if you press the weapon key again while holding a torch. This could also be used to resolve the maddening problem of not being able to auto-switch back to your real weapon after using a pick or probe and press weapon key again (or you used the last use of the pick/probe and don't have another of the same type). It should also be applied to your "magic hands" after you cast from a scroll and it was the last scroll of that sort – you should go back to the last spell or magic item you used before, instead of putting your hands down, which has got me killed at least 10 times. Would be nice is pressing magic key again after using a scroll and still in scroll mode put you back on your last actual spell or pre-scroll cast-on-use item.
The second-best thing would be to switch back to that weapon after manually putting the torch (or pick or probe) away or dropping it.
I cannot confirm the claim that "during combat NPC will have both weapon and torch equipped" (or more like I can "dis-confirm" it). I use companion mods constantly, and give them torches. When fighting, their torches are put away. If you're seeing torches briefly during [un]equipping animation, that's just the NPC AI cycling through what to equip. It could be tweaked to not show a brief torch flash, but it's hardly crucial. It's possible if the weapon is one-handed and they have no shield that they might use the weapon in one hand and the torch in the other, but that wouldn't be a bug. I just tested again, and my companion NPCs with two-handers put the torch away. If there is a bug there, it must be more specific, like when they don't have a shield in inventory? I didn't try every possible combination of gear and weapon type.
#3 Updated by Dark Locq about 2 months ago
Followup: I can confirm that an NPC with a one-hander and no shield will fight, in dark areas, with weapon in one hand and torch in the other, but will put away the torch and use the shield if he has one. I remembered that a mod, Discoveries and Adventures by JMK, has a Royal Guard and a High Ordinator duel in Old Mournhold: Battlefield, and I just watched it and it works exactly this way (i.e., as one would expect).
In my previous comment, I noted "I use companion mods constantly, and give them torches. When fighting, their torches are put away." All my companions get shields, so this is also expected behavior.