Incorrect exploration algorithm in map_grid.cpp

[lucamozza]

In base_local_planner/src/map_grid.cpp the function computeTargetDistance is used to compute the minimum distance between each cell and the plan/goal.
From my understanding, in the following lines we are exploring from current_cell and checking its four neighbors, which are represented by the check_cell variable.
Checking a cell consists in updating its distance if the distance coming from current_cell is lower than the current minimum one, and adding the check_cell to the queue of cells from which the expansion has to be performed.
The distance is not updated if the cell was already marked as explored.

navigation/base_local_planner/src/map_grid.cpp

Lines 266 to 275 in 6e9de3f

	if(current_cell->cx > 0){
	check_cell = current_cell - 1;
	if(!check_cell->target_mark){
	//mark the cell as visisted
	check_cell->target_mark = true;
	if(updatePathCell(current_cell, check_cell, costmap)) {
	dist_queue.push(check_cell);
	}
	}
	}

In this line of reasoning, I think that the cell should be marked as explored once we explore from it, that is we should mark current_cell, not check_cell as it is done currently.

navigation/base_local_planner/src/map_grid.cpp

Line 270 in 6e9de3f

check_cell->target_mark = true;

In the current version, distances are never updated, they will remain to the value set in the first iteration.

Am I getting this right?
Are there any other reasons why this choice was made?