Configuration R- and S- labeling problem

[porn at ATC.ATCCU.CHULA.AC.TH]

Dear Sir,

  
  We have a problem for calling the enantimeric configuration of a chiral
carbon of our molecule. Incidentally, Insight II denotes what we
would call S-emantiomer as R (!). And even more strangely, as soon as
this molecule has been protonated, it now denotes this same enantiomer as
S. Who can explain this?

  Cheers
Thep