fix categorical and datetimetz (when in dataframe + converted to object)

pandas/core/internals.py

@@ -2421,13 +2421,15 @@ def concat_same_type(self, to_concat, placement=None):
         Concatenate list of single blocks of the same type.
         """
         to_concat = [blk.values for blk in to_concat]
-        values = _concat._concat_categorical(to_concat)
+        values = _concat._concat_categorical(to_concat, axis=self.ndim - 1)
 
         if is_categorical_dtype(values.dtype):
             return self.make_block_same_class(
                 values, placement=placement or slice(0, len(values), 1))
         else:
-            return make_block(values, placement=placement or slice(0, len(values), 1))
+            return make_block(
+                values, placement=placement or slice(0, len(values), 1),
+                ndim=self.ndim)
 
 
 class DatetimeBlock(DatetimeLikeBlockMixin, Block):
@@ -2711,13 +2713,14 @@ def concat_same_type(self, to_concat, placement=None):
         Concatenate list of single blocks of the same type.
         """
         to_concat = [blk.values for blk in to_concat]
-        values = _concat._concat_datetime(to_concat)
+        values = _concat._concat_datetime(to_concat, axis=self.ndim - 1)
 
         if is_datetimetz(values):
             return self.make_block_same_class(
                 values, placement=placement or slice(0, len(values), 1))
         else:
-            return make_block(values, placement=placement or slice(0, len(values), 1))
+            return make_block(
+                values, placement=placement or slice(0, len(values), 1))
 
 
 class SparseBlock(NonConsolidatableMixIn, Block):

pandas/tests/internals/test_external_block.py

@@ -4,7 +4,8 @@
 import numpy as np
 
 import pandas as pd
-from pandas.core.internals import Block, BlockManager, SingleBlockManager, NonConsolidatableMixIn
+from pandas.core.internals import (
+    Block, BlockManager, SingleBlockManager, NonConsolidatableMixIn)
 
 
 class CustomBlock(NonConsolidatableMixIn, Block):