Photoshop: Mixer Brush Tool merging layers

Fixed in CS6 or later.

Could go into a little more detail here?

I created a document with 6 layers plus the background layer. I turned off the visibility of the middle layers (3 and 4). Close the file, switched to the Mixer Brush and reopened. Nothing happened.

Would like to be able to recreate the behavior if possible. Give us the exact step by step process please.

What version of OS X are you using? What video card do you have? This may be part of the larger graphics driver issues with Lion and specific video cards.

OS X version 10.6.8, video card NVIDIA GeForce 8800 GT.

I already uninstalled and reinstalled Photoshop CS5 and the problem still exists.

With the Mixer Brush tool selected, I try to open a large image file (over 150 MB)
and Photoshop automatically tries to merge layers. Smaller images open OK.
But in any case, turning off a layer's visibility takes several seconds. Photoshop
seems to require excessive processing with the Mixer Brush selected. This may
just be an issue that is peculiar to my machine and I will just have to live with it.

It sounds like it's file specific if I'm following your steps correctly. Can you post the file you're trying to paint on? Or can you make a video of your entire screen while this is happening?

I created a QuickTime movie of the glitch. How do I upload it?

I have found that the Mixer Brush-Merge Layers problem occurs when an image
file has more than four or five adjustment layers. The number of pixel layers in an image doesn't seem to matter. The problem doesn't occur when there are only
five or four or fewer adjustment layers. But, even then, there is still a long
response time for turning a layer visibility off or on. This was demonstrated in the
two QT movies i emailed to Jeff.

I'm still investigating. I'm trying to build a document similar to yours that exhibits the behavior.