Fused volume rendered images do not rotate in synchrony, seemingly don't reflect reality

i managed to fuse a ct to a spect image and display the resultant fused image as a 3d volume .
however if i rotate the fused image it appears asif it does not reflect reality , asif they still behave as seperate volmes ,(do not move in sync) i have "closed the chain rings " but it still appears something is lacking ,
ie - i know the spect focus is in the spine - so if the other volume(ct) has opacity set to 1 i should not see the spect focus in the spine - looking from the front , or if i know it is on the right it should not show if i look from the left - would appreciate some assistance

You need to use the experimental multi-volume rendering feature for this. It has some limitations. If those limitations are unacceptable for you then you can combine your volumes into one volume and then render it as a single volume.