trunk & 1.8 head.

create two templates (let's say t1 & t2), link t2 to t1.

create a host, link it to t2, save.

reopen host, remove t2 linkage, add t1, save :

[ CTemplate::massAdd ] Circular link can not be created
[ CHost::massUpdate ] Can't link template
[ CHost::update ] Host update failed

such an operation should always unlink removed templates first, then add new ones.