RooDataHist - 2 histograms, entries are doubled

Dear everyone,

I have a problem with RooDataHist when I am importing two TH1F histograms:

//Build categories
 RooCategory sample("sample","sample") ;
 sample.defineType("physics") ;
 sample.defineType("control") ;
//Import data
 RooDataHist combData("combData","combined data",x,Index(sample),Import("physics",*hsig),Import("control",*hsdb)) ;

When I now plot my intial data and the data from the RooDataHist I have a different number of events (the RooDataHist has twice as much entries):

RooPlot* frame3 = x.frame() ; 
combData.plotOn(frame3,Cut("sample==sample::control")) ;
frame3->Draw() ;

When I add 3 histogramms, they are scaled by a factor of 3.
Is there a possibility to avoid the scaling?

Thank you and kind regards