different colors of buildings with same tags

[Klumbumbus]

I noticed some strange behavior how JOSM renders colors. The problem is that buildings with exact the same tags look different if there is an landuse=residential area around. It's a bit hard to explan it in detail for me, so I made a video, where I show the problem:
​http://youtu.be/55TtC4wQAXg

To eliminate side effects I disabled the JOSM internal Mappaint style and used a mappaint style with the following code (although, the problem also occours with active internal JOSM mappaint style):

area["addr:housenumber"]
{ 
	fill-color: green;
	fill-opacity: 0.7;
	text-color: black; 
	font-size: 16;
	text-halo-radius: 8;
	text-halo-color: green;
	text-halo-opacity: 0.7;
	text: tag("addr:housenumber");
}

area[landuse]
{
	fill-color:	#f0f0f0;
}

I want to describe, what I do in the video:

I download some data. Notice that I do not download any node of the landuse=residential area, which is around, so, the landuse area is not dowloaded. Until this point everything is ok. The buildings with number 15 and 17 look the same. Then I download the landuse area. Now, there is the landuse=residential area around the buildings. You can see that the building with number 17 is brighter and the building with number 15 is darker (fill-color and halo-color). Then I copy and paste building number 15 and it has also the brighter colors.

Then I move an node of the landuse, so there is now landuse=meadow around the buildings. You can see that the dark green building in the middle switches also to the bright color version.

Then I delete the meadow area, and move the node again. When there is no landuse over the buildings, the two outer buildings (left 15 and 17) switch to the dark color version.

I'm not sure, wich color version is correct, but these buildings should always look the same since they have got the same tags. (I mean, colors can be different with and without landuse around, but there should not be differences between the buildings with each other). Are you able to reproduce this problem?
I tried it on 2 different windows computers with latest stable JOSM. The example area, which I show in the video is here: ​http://www.openstreetmap.org/#map=19/50.81339/12.97180