This is a problem I've known about for a few years so could possibly have been reported before but I couldn't find any threads regarding it so with V6 approaching thought I'd bring it up, if you set a player.level.var Clientside while on a GMAP it seems to work at first however wear off once you travel far enough away from your position at the time of the variable being set.
The obvious work-around to this is that you can accomplish the same thing without this problem by setting a player.gmap.var, however would it be possible for the level object to act the same in future?
On client-side the player.level is the single .nw map part, and you can access the gmap by player.gmap. On server-side it is not managing the map parts, so player.level is pointing to the gmap instead.