map display/overlay, how to share it

Hi,
Many time when I do any area (in map or regular levels area)
I noticed that sometime I can benefit and see the already explored area, sometime not.
How does the trick work?

Exemple: I start the map with my main, clear it a bit, then tp some of my alts... sometime the map is shared and the one teleporting in can see the explored part of the map (area already visited) sometimes not.. :$

Any hints?

So nobody know?
Maybe im not clear:
Let say you do a map and then invite a friend, sometime he can see on his minimap the already explored area, sometime not.
Do you know why?

thought about it last week and still have no idea :)

Usually, I don't see the map when I join a group (which I do rarely), I just see those green x in the distance.

I think you see it when you change characters because it's saved in a temp file or cache or something. You should never be able to see the explored parts of a party member.

i usually play with 2 to 3 accounts, leveling some in vorici area, other in haku, sometime is clear sometime its not.

It is'nt even related to computers.. i use both on my main and the last one on an older computer, even on the same machine there is now rule.

I undertands that you could not see what's meant to be "fog of war" but for the already explored it would be better to know how it work.

Hope one dev (dream about it) and give us the know how :)