Because Arkhalia is using Community Patch there are several ruleset changes in play from this source. While all these changes are considered to be a bugfix and to be considered as a new standard, there are still players who doesn't know about this and then reporting it as a bug.
So for reminder:

• Spell Immunity has priority over Spell Mantle. This means that if you have both Globe of Invulnerability or some other effect or item granting you immunity to certain spell levels or schools, when a spell from such level or school is cast against you, it will be blocked by immunity and won't deplete Spell Mantle.
• AOE spells (ie. various clouds and auras) will not be blocked by Spell Mantle at all.
• All persistent AOEs will now disappear when their caster becomes invalid (player left game, monster died and disappeared).
• Musical instruments cannot be used under silence and has 20% chance to fail if the player is deafened. (Musical instruments are all miscelanious items with an image of some musical instrument limited to bards.)
• DC for using scrolls via Use Magic Device skill is now 7+(3*InnateLevel). InnateLevel is level of the spell ie. 0-9.
• Reading scrolls under blindness effect (and without True Seeing) will fail.
• AOE effects created from special abilities such as auras were set to be permanent, supernatural and undispellable. Effects, that are based on the AOE presence are now also undispellable. (For example, it's no longer possible to dispell effects of the silence aura without dispelling the aura first.)
• Fear aura will trigger only once per each creature entering. No more infinite chasing and rolling of 1s.
• Assassin can take Epic skill focus: use magic device as a general epic bonus feat.
• Whip can be dual-wield.
• Flying creatures are immune to some ground spells and effects such as grease or caltrops.

Note: This is not a full list but rather a short summary of the most important changes. For full list, refer to the Community Patch documentation.

• Fixed NWN limitation that prevents spontaneous spellcasters (bard, sorcerer, favored soul) to gain new spells know from prestige classes enhancing spellcasting (palemaster, stormlord, mystic theurghe…). Upond finalizing the level up process a custom spells known selection GUI will show up where you can select additional spells.
• Magical Staff will is now one-handed weapon even for smaller races.
• Damage Resistance itemproperties stacks with each other.
• All non-physical damage bonuses are subject to the damage immunity and damage resistance. (In vanilla NWN some of these bonuses ignore it)
• Gloves can be enchanted by spells.
• Character will automatically equip a new stack of throwing weapon when you throw the last one.
• AOE stacking is disabled. You can only have one AOE of same type present at the same time.
• Duration of all disable effects from all sources (stuns, paralysis, fear, etc.) is now capped at 3 rounds, or 6 if the spell was extended. Petrification is excluded from this rule and is still permanent. Note, that there might be items and monsters that allows to expand this limitation.
• Poisons can stack.
• Flying creatures are immune to traps.
• AOE spells ignore spell resistance (and spell mantle), only spell immunity applies.
• Immunity to ability decrease doesn't affect penalties from items.
• Curse effect ignores immunity to ability decrease.
• Poison and disease effects ignore immunities to those effects (for example ability decreases will ignore immunity to ability decrease), the only way to avoid that is to get immunity to poison or disease specifically.
• Immunity to slow grants also immunity to speed decrease and vice-versa.
• Hardcore Uncanny Dodge rule.
• Initiative has a real meaning. The one who wins the intiative roll, considers his opponent to be flatfooted for all attacks in his first flurry. This doesn't mean that the loser is fully flatfooted, he is flatfooted only towards the winner of the initative.
• Creatures immune to critical hits does not need to be automatically immune to sneak attacks as well.
• Characters get double the bonus damage when using Power Attack feat with two-handed weapons. For this purpose, two-hand weapon refer to any non ranged weapon that prevents to use shield or weapon in off-hand. This means that small races such as halfling will get this bonus as well.
• Damage coming from itemproperty OnHit: Wounding is no longer subject to immunities, reductions or resistances.

Positive:
- Bard Song: you are under effect of Bard Song ability
- Waterbreathing: can breathe under water (immunity to drowning + ability to enter (under)water areas)
- Flying: immunity to some ground spells and effects such as grease or caltrops
- Increased GP gain
- Increased XP gain

Negative:
- Fatigue: -2 strength, -2 dexterity, 50% decreased movement speed (debuff from Barbarian Rage/Frenzy)
- Cursed Song: you are under effect of Curse Song ability
- Webbed: you are embroiled in web
- Raised from dead: -4 attack bonus, -4 all skills, -2 all saving throws, 20% spel failure, 50% decreased movement speed
- Bleeding: unresistable damage each round and 50% less healing received from all sources
- Cannot be Hasted: debuff under which you cannot be hasted
- Magically Aged
- Dimensional Anchor - teleports into other areas won't function