Overlap and data loss on WindowedBolt based on Duration

The attachment is my test script, one of my test results is:
```
expired=1...55
get=56...4024
new=56...4024
Recived=3969,RecivedTotal=3969
expired=56...4020
get=4021...8191
new=4025...8191
Recived=4171,RecivedTotal=8140
SendTotal=12175
expired=4021...8188
get=8189...12175
new=8192...12175
Recived=3987,RecivedTotal=12127
```
This test result shows that some tuples appear in the expired list directly, we lost these data if we just use get() to get tuples, this is the first bug.
The second: the tuples of get() has overlap, the getNew() seems alright.

The problem not happen definitely, may need to try several times.

Actually, I'm newbie about storm, so I'm not sure this is a bug indeed, or, I use it in wrong way?