Unexpected changes

When I hit Ctrl + Alt + 0, my spread is stretched vertically to fit my workspace, but it is not horizontally centered anymore in the workspace.
Does anyone now why is that?
Previously my document grid was displayed on the whole surface of my workspace, but now it extends only until the bleed.
Does anyone know why is that?
Sometimes my left bleed is under the toolbar, and I cannot re-center my spread when hitting Ctrl + Alt + 0.
Why is that?
Thanks in advance.
