Comparison after pd.concat
Hello,

I am wondering if the following is considered to be a bug.

I have two Series a and b. They are the same.

However, after merging with a third Series c, the equality no longer hold.

```
a = {"open": 1, "high": 2, "low": 3, "close": 4, "UpBand": 4, "MidBand":3, "LowBand":5}
b = {"low": 3, "close": 4, "open": 1, "high": 2, "LowBand": 5, "MidBand":3, "UpBand": 4}
c = {"haha": 5, "hello": 2}

t1 = pd.Series(a)
t3 = pd.Series(c)
t2 = pd.Series(b)

t13 = pd.concat([t1, t3])
LowBand    5
MidBand    3
UpBand     4
close      4
high       2
low        3
open       1
haha       5
hello      2
dtype: int64

t32 = pd.concat([t3, t2])
haha       5
hello      2
LowBand    5
MidBand    3
UpBand     4
close      4
high       2
low        3
open       1
dtype: int64


t1 == t2
LowBand    True
MidBand    True
UpBand     True
close      True
high       True
low        True
open       True
dtype: bool


t13 == t32
LowBand     True
MidBand    False
UpBand     False
close      False
high       False
low        False
open       False
haha       False
hello      False
```
