After having failed to use tech support (critical error - please check "event viewer"), this is the bug I wanted to report:

This works:
arr = [1,2,3,4,5,2,1,2,3,999,999]
bpd = createboxplotdata(arr, OUTLIER=out)
o = boxplot(bpd, OUTLIER=out)

This does not work (IDL does not draw outlier point):
arr = [1,2,3,4,5,2,1,2,3,999]
bpd = createboxplotdata(arr, OUTLIER=out)
o = boxplot(bpd, OUTLIER=out)

(tested under Windows 10, IDL 8.6.0)