have templates and host linked like this :
t1 -> t2 -> h1

one item on t1.

open properties of t2, add h1 to be linked to t2, try to save - it fails and says "template t1 already linked to h1"

that is mighty confusing - maybe it's better to show the template that is closest to the host, not the one item originates from ? (as that at least can be seen in the hostlist and host properties)