During free hand writing, it's really easy to have two strokes coincide together, the previous created drawing annotation shouldn't be triggered by the next drawing attempt. Refer URL for the reproduce screen recording Reproducible: Always Steps to Reproduce: N/A Actual Results: N/A Expected Results: N/A
I've noticed that Adobe Reader XI have this bug too, wish that Okular can solve it.
I just tested this on Okular 1.5.3 and was unable to reproduce your issue with a previously created annotation, and freehand drawing.