A event recorded event in the default stream zero cuplaEventRecord(event,0) is not blocking all other streams.
This behavior is different to CUDA.
Note: with CUDA 7 the behavior of the default stream can be changed that each thread can have it's own default stream. https://devblogs.nvidia.com/parallelforall/gpu-pro-tip-cuda-7-streams-simplify-concurrency/
This should not interesting because cupla is not thread save :-)