Thanx a lot for fixing bug
[#26424], that's really fast! :)
This is something related to that bug:
1. render a scene in slot 1
2. swap to slot 2 make a little change to the scene (like move your camera a bit) and render again
3. swap to slot 3, make a little change and re-render
4. swap to slot 4, change again your object position then render
5. have a look at the render slots cycling them with J key, they're all full with successive renders...
6. ...now hit Ctrl+Z to undo last camera/object move and all render slots suddenly became empty except the current one
No .blend attached because even the startup file is good to testing, anyway you'd have to follow those steps to have at least some render in your slots.
System specs:
Linux 64 bit
Nvidia card with GeForce 260.19.36
Blender SVN 35433 compiled with scons and Blender 2.56a 64 bit official Beta
Thanks a lot for your hard work!