put data and then get it , but it returns null in sometimes

[????????]

Hi all,
     I have encountered a very strange problem?? described as follows:
     first ,  put(1, 2) to the cache in sync mode and the cache is atomic mode; 
     then, I immediately invoke get(1) in sync mode to get key=1, expect it 
returns 2;
     however,  it returns null;
    
    this question is random appearance,  but I have encountered a lot times;
    
    Is there anybody have encountered this question,  And how I can solve it ? 


   Thanks!