If I don't call clear(); on the list before I assign it something else, there's a memory leak.

	towrite->brushes.clear();
	towrite->brushes = g_edmap.m_brush;

I tried reproducing the problem with lists of a simple dummy class but it doesn't leak memory like the code above.

The variables above are of type list<EdBrush>.

Any ideas why?

class EdBrush
{
public:
	int m_nsides;
	EdBrushSide* m_sides;
	int m_nsharedv;
	Vec3f* m_sharedv;	//shared vertices array
	int m_texture;	//used to determine brush attributes
	EdDoor* m_door;
	
	EdBrush& operator=(const EdBrush& original);
	EdBrush(const EdBrush& original);
	EdBrush();
	~EdBrush();
	void add(EdBrushSide b);
	void setsides(int nsides, EdBrushSide* sides);
	void copysides(int* nsides, EdBrushSide** sides);
	void removeside(int i);
	void collapse();
	void remaptex();
	Vec3f traceray(Vec3f line[]);
	void prunev(bool* invalidv);
	void moveto(Vec3f newp);
};

Do your assignment overload make sure to delete any memory already allocated by the object you assign to?

If you don't, that could be your problem.

You are correct.