Is the cumulative shifted way off on all new polylengths that you do? If so, draw one polylength, then drag the cumulative measurement text to where you would like it (drag it by pressing SHIFT then clicking and dragging on the text). Then, with the polylength still selected, go back to the properties panel and click the "Set as Default" button at the bottom and see if that changes it. Note: that will also set line type, color, width, opacity, etc to your default. That may work.