evaluation - Unexpected behavior of Set

Set doesn't work in some conditions.

(* Input separately, whithout "()" or ";" *)

In[1]:= expr1 = x + y == 0 && x > 0
Out[1]= x + y == 0 && x > 0


In[2]:= expr2 = x + y == a && x > 0
Out[2]= x + y == a && x > 0

In[3]:= {expr1, expr2}
Out[3]= {expr1, x + y == a && x > 0}

Evaluating again would make the assignments successfully.

(* Chinese Edition *)


In[4]:= $Version
Out[4]= "10.3.1 for Microsoft Windows (64-bit) (December 21, 2015)"

I'm wondering if I have done something wrong. However, I found that Mathematica returned to normal behavior when I minimized the Suggestions Bar.

Any ideas?