dataLabel colors revert to black on rangeBar with rangeBarGroupRows with more than 50 elements

[mmarkholt]

I'm using chart.type: "rangeBar" with several hundred elements, and plotOptions.bar.rangeBarGroupRows:true, with the default theme.
I set dataLabels.style.colors to ['#ffffff'], which works for the first 50 elements. The data label on every bar beyond 50 appears in black.
I've tried setting plotOptions.bar.dataLabels.style.color and colors, as well as plotOptions.dataLabels.color and colors, but that doesn't fix the issue.
Has anybody else seen this behaviour please? Am I missing a magic incantation or is there some kind of hardcoded limit?
Mark