I'd like to just confirm that a problem I am having in QGIS 2.10 is not unique to me.
I am using the Layer Order panel to control the rendering order of layers in my projects, it's very useful when working with lots of layers. However in QGIS 2.10, when I move a layer it does not change the layer's rendering order, it simply duplicates the layer (see below, notice all the duplicated layers).
The Value Tool also sees the duplicated layers (if it's a raster). The layers are not duplicated in the 'Layers' panel. It only happens when I tick the 'Control rendering order' tick box at the bottom of the Layer Order panel.
If others are affected I'll submit a bug report.