pyspark dataframe not maintaining order after dropping a column

Question

I create a dataframe:

df = spark.createDataFrame(pd.DataFrame({'a':range(12),'c':range(12)})).repartition(8)

its contents are :

df.show()
+---+---+
|  a|  c|
+---+---+
|  0|  0|
|  1|  1|
|  3|  3|
|  5|  5|
|  6|  6|
|  8|  8|
|  9|  9|
| 10| 10|
|  2|  2|
|  4|  4|
|  7|  7|
| 11| 11|
+---+---+

But, If I drop a column, the remaining column gets permuted

df.drop('c').show()
+---+
|  a|
+---+
|  0|
|  2|
|  3|
|  5|
|  6|
|  7|
|  9|
| 11|
|  1|
|  4|
|  8|
| 10|
+---+

Please help me understand what is happening here?