The property SequenceFilePath "remembers" the last path you entered or wrote via the API. If you set the UseCurrentFile to TRUE, the value is ignored, but not overwritten. ther same happens in the Sequence-Editor. if you enter a string, then check the UseCurrentFile Flag, and uncheck it again, the entered path appears again.
So this is the intentional behaviour.
To get the path of the used sequence file you would have to check the UseCurrentFile flag first. If it is checked, use the path of the used sequence, if it is unchecked, get the SequenceFilePath property.