I use QwtPlot to show a time series (i.e. I append a new point every 1" and the x axis autoscales).
I set x axis with major ticks only (no minor ticks) and everything is ok for a while.
After more or less 50", when I add a new point, one minor tick appears (at least its look-and-feel is the same as a minor tick) unexpectedly.
This "minor tick" seems to be "attached" to the point and it scrolls together with the x axis.

Do you have ideas on what is it?
Is there a way to avoid it?

I see the behavio with Qwt 6.1.3 under Windows.