[9.11] What's the deal with scrolling text set to background transparent?

Rather alarmingly, using any ink other than copy for a scrolling text field, the background will scroll along with the text and new lines of text scrolling into view will display with a plain white background. This is what's known in the trade as a bug.

The only way I can see to avoid this is to create your own custom scrolling field script as in 9.10 above. (If someone has a better solution, let me know!)