I was able to find some more runs with varying deadtimes and rates. Good news, is that as long as the deadtime is kept under 30%, all the normalizations seem to agree (even up to 47% DT and a 9kHz rate). So maybe that one run was just an anomaly. Regardless, I wouldn't want to find the point where it becomes an issue!
Figure 1
DT_COMP1.pdfFigure 2
DT_COMP2.pdf