Some net names changed?

Hi,

I have some identical net labels in two different schematic pages. When I try to create Differential Pairs I see that one of them changes. for example if I have CLK1_P,CLK2_N in two pages I see them in "create Diff paris" utility in this way : CLK1_p,... CLK1_P_0402355666 !. So weird!. Shouldn't I have a unique net label called CLK1_P?!. why there are two labels ?!. How can I show to OrCAD Capture that these two nets are the same?

Thanks,

Hossein