The problem usually occurs if that target BCCH is interfered. Since MS has to listen to that BCCH and send the decoded BSIC. If two neighbours closeby have the same BCCH with different BSIC then MS shall either not be able to decode bsic or show two different BSICs at different locations near sites.
If BSIC is not decoded / BSIC is decoded other than the one specified in the Neighbour list HO shall not be trigerred.