yes, it is very strange.
Do you have the (tems?) log of this behaviour ?
if yes, then you should check some parameters of this distance cell:
Regarding MNC/MCC : are they correctly set ? or are they identical to your own PLMN’s values ?
Regarding BCCH : is this frequency the same as one of your neighbours?
You could tune the parameter NCC_permitted, in order to have only your own NCC allowed for that particular cell.
Another (far-fetched) theory : the distant PLMN is considered as a “home plmn” in your SIM card. If that’s the case, then you have a big problem, as this is a hardcoded setting (in the SIM) that cannot be modified remotely.