Bug type: Non-KMS maps don't function properly.
Brief bug summary: Maps that don't exist in the Korean version of MapleStory lack features.
1. Familiars don't affect mesos/drop rates in maps that aren't in the Korean version of MapleStory.
Example of familiars: Big Spider (50% drop rate), Eye of Time (% mesos rate), Wolf Underling (80%? drop rate)
Example of maps: Mori Ranmaru's drops aren't affected by familiars, as he doesn't exist in Korean MapleStory.
However, drop buffs such as Holy Symbol (Bishop), Lucky Winter, drop coupons or 2x events affect drop rate there.
2. Maps that aren't in Korean MapleStory don't get affected by level reduction.
You get the same amount of mesos for kiling a Blackgate City mob at whatever level are you (180, 220, 240). Maps that are in Korean MapleStory though get reduction for being about 20 or more levels higher than the mobs.
Quests that need you to kill "mobs near your level range" also count as long as the mobs don't exist in Korean MapleStory. For example, a level 250 player can finishg such quests by killing in Mysterious Path 3 or Northern Heights (popular mesos farming maps in Reboot world).
3. Elite monsters/bosses won't spawn in maps that don't exist in Korean MapleStory.
4. Runes will not spawn in maps that don't exist in Korean MapleStory.
Edit: Might be a bit off. Refer to AKradian's comment for additional information! http://forums.maplestory.nexon.net/discussion/comment/36114/#Comment_36114
There might be more that I missed out.
Steps to reproduce: Kill monsters in a map that doesn't exist in the Korean version of MapleStory. Example: Wolf Spider Cavern in the Big Ben of New Leaf City.
Character name: Irrelevant. This isn't a character specific issue.
Character level: Irrelevant. Level doesn't matter.
Character job: Irrelevant. Happens to every class/job.
World name: Irrelevant. Happens in every world, in both Europe and North America.
Date and time of the incident: Irrelevant. It's been like that for years.