Platform: PC
ISP: Movistar
Type of Internet Connection: ADSL
Internet Connection Speed: 10Mb/s
Date & Time: Aug. 28, 2011 23:12 GMT+2
Frequency: Once (Did not reproduce)
Character Name: Umo Heima
Race: Highlander
World: Gysahl
Class/Skill Rank: Lancer/32
Physical Level: 50
Area and Coordinates: Central Shroud>Humblehearth (25, 31)
Party or Solo: Solo
NPC Name: N/A
Monster Name: Dire Dormouse
In-Game Time: 22:01
Steps:
1. Activate "Reforesting Humblehearth" guildleve by Humblehearth's aetheryte.
2. Locate guildleve's monsters and engage them. A party of 1 Dire Dormouse and 1 Nutcracker Squirrel was engaged.
3. Wait for Dire Dormouse to cast "Nutshell" ability.
4. As long as there were more parties of Dire Dormouse + Nutcracker Squirrel on range, the Defense Up effect was granted to all the monsters (4 in this case).

I guess the effect must be granted only to the monsters on the party (the red ones if they are correctly engaged). Feel free to close the thread if this is working as intended.