Elastic-Perfectly Plastic in Abaqus Explicit

Dear Mechanical Engineers,

It's my pleasure to be one of your group. I have a question in Abaqus Explicit and all my friends recommended me to as iMechanica as the explicit Abaqus is more popular to you than us as civil engineers.

I’m trying to simulate a tensile test for an elastic-perfectly plastic material as a quasi-static analysis in Abaqus Explicit. I have solved the same problem in Abaqus Standard and the results were fine as follow.

In Abaqus Explicit I have a problem which is the trend of the stress-strain is not elastic-perfectly plastic like in Abaqus Standard. In Explicit the load arrived to the yield point and then released instead of going constant when the strain increases as you can see in this image.

As you knew that in the elastic-perfectly plastic material the stress and strain increases up till the yield point then the stress become constant however the strain increase.

This trend I got from standard. However in explicit the stress arrived to the yield point (the same point exactly) like in standard then suddenly go to around zero stress vertical and then the strain increases again under (around zero) stress.

I solved the same problem in standard and explicit. Everythin is the same (material parameters, BC, and tensile displacement rate, etc.). There was only one different that I used a mass scale factor in abaqus explicit to speed the analysis because I'm applying a displacement of 180mm in 3600 sec and as you knew I can't do it without acceleration as it may take long long time.  

I appreciate if someone can explain to me how to solve this issue in Abaqus explicit however I used the same parameters like in Abaqus standard but I don’t know why this happened.

Thank you,