Example:

import pyqtgraph as pg
x = pg.np.linspace(0, 1, 1000)
plt = pg.plot(x, x**20)
plt.setYRange(0, 1e-8)

Drag the plot downward and it begins to flicker when the plot crosses the viewbox boundary.

This appears to be due to a Qt bug; report filed here:
https://bugreports.qt-project.org/browse/QTBUG-36720

Original report discussion is here:
https://groups.google.com/forum/#!msg/pyqtgraph/oSLHg8N-0JE/-7kT0Vgg4DoJ