Spark Label Flickering at 100% width (or: any other non explicit width) when frequent appending occurs (typewriting effect, text edit)

Attached small example file, generated in latest relase sdk (4.5.1, but also seen in 4.1)

Steps to reproduce:
1. Create Spark Label with relative width (e.g 100%)
2. Frequently append text in that label (no matter what frequency)

Actual Results:
Label is flickering

Expected Results:
No flicker at all.

Workaround (if any):
Try the same with an explicit width (100px). Everything is fine.