bmap_rendertarget is specifically for using multiple render targets in one shader. It's also somewhat redundant (it works, but VIEWs render targets can now be manipulated/changed through their target1...target3 BMAP pointers). These will only work if your pixel shader has "out float4 colour1: COLOR1" and the like to render to additional render targets.

Try using view.bmap, instead. This is the easiest means of render-to-texture, as the view's output will go straight to that bmap. In the meantime, I can't resist: I'm going to try a quick test.