Hello,
I’m having a little problem with the compositor. I must have accidentally pressed any key(s) and now every time I go on a viewer, the result gets re-rendered. Pretty annoying. I hope there is an easy answer for this.
Lorenz
It’s functioning as advertized. Any time you select between two different viewer nodes this will happen. It’s because the node results are held ina a sp-are render buffer and selecting one forces the other out of the buffer resulting in a need to re-post precesds the newly selected viewer node.
Sry, but I’m absolute sure, that this behavior wasn’t there before. I could compare a viewer to another as soon as I clicked on it.
Hmm, I discovered that this problem only exists in the specified scene. So, either it’s no general function, or the scene has a crack.
Disable the “Free Unused” button.
It was and is disabled. But nice thought. I never used this option, so maybe that’s it, either it’s obvious not activated.
Can you upload your .blend?
Yeah, here it is. But the scene isn’t important anyway, because it’s just a keying-test. But I am interested anyway. 
http://rapidshare.com/files/164448148/re-rendering_compositor.blend.html
(Tried to reply yesterday, but somehow it didn’t appear.) It’s only a keying-test, so nothing important, but I’m interested anyway.
http://rapidshare.com/files/164711265/re-rendering_compositor.blend.html
I’m not familiar with this forum. Is it right, that my reply with a link to the file, first gets checked by an admin before it appears?
There’s a message on here called State of the Forum that discusses that issue…seems they’ve been having increased trouble with spammers lately so your post may have been flagged.
OK, that’s the way how it works, I hope.
Just a keying test, so nothing important, but I’m interested anyway. 
Attachments
re-rendering_viewer.blend (236 KB)
It seems to have to do with your movie/image files. When I replaced all their connections with a render layer output the problem vanished. As I replaced the image node connections (one by one) clicking on the viewer nodes progressively requires more post calculation. I can’t swear that this is a bug but I don’t see any reason why blender can instance a renderlayer and not instance a movie. Ask some of the coders on the forum and, depending on the reply you receive, possibly report this in the bug tracker.