error in plotting Y vs Y

Hi all,

I have 2 functions that I want to plot vs each others. I used WaveVsWave function in the calculator and Y vs Y option in the x-axis right-click menu. They both usually work but sometimes the resulting graph shows only 1 point, is this a bug? I'm using virtuoso 6.1.7. The following image shows what I mean, on the left are the 2 graphs and on the right is the result of Y vs Y option

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I tried exporting both graphs to .csv files and combining them in excel but I couldn't import the resulting .csv file back into the result viewer, how can this be done too? if it works I can use it as a workaround when this happens.

P.S.: both graphs are generated vs. time in the same simulation & corner so they both have the same number of points.

Thanks in advance