When using a QwtDateScaleEngine with data ranging from 0m0s to 5m59s makes a scale that does not end with a major tick, whereas the Floating attribute is never set. Major step is 2m, medium step 1m, and minor step 30s. The scale seems to end around 6m40. Could it be 400 seconds ?
With data ranging from 0m0s to 6m29s, the scale ends with a major ticks, but it is 6m0s, so the curve is not completely displayed