TypeError during DataShader aggregate creation between Python 3.5 and 3.6 environments

Question

I've been working with the bokeh/datashader dashboard in python 3.6.X developing some additional functionality into the dashboard project. When the project is executed in a 3.5.2 Python environment I run into a TypeError: data type not understood during creation of an aggregate that is not present in the 3.6.X execution.

agg = method(self.df[(self.df['time_position'] >= time_start) & (self.df['time_position'] <= time_end)
                                 | (self.df['time_position'].isnull())], x_field, y_field, ds.count_cat(agg_field))

with x_field and y_field as float64 web-Mercator longitude, latitude fields from a Pandas DataFrame and time_start and time_end as float64 values as is the DF['time_position'] field.

A simple test with method as Canvas.line

agg = method(self.df, x_field, y_field, ds.count_cat(agg_field))

removing the df (DataFrame) indexing request yields:

Traceback (most recent call last):
File "C:\Users\user\AppData\Local\Continuum\Anaconda3\envs\TrendingAnalysis_GUI_python352\lib\site-packages\IPython\core\interactiveshell.py", line 2910, in run_code
    exec(code_obj, self.user_global_ns, self.user_ns)
  File "<ipython-input-3-c9d8810a25e0>", line 1, in <module>
    agg = method(self.df, x_field, y_field, ds.count_cat(agg_field))
  File "C:\Users\user\AppData\Local\Continuum\Anaconda3\envs\TrendingAnalysis_GUI_python352\lib\site-packages\datashader\core.py", line 202, in line
    return bypixel(source, self, Line(x, y), agg)
  File "C:\Users\user\AppData\Local\Continuum\Anaconda3\envs\TrendingAnalysis_GUI_python352\lib\site-packages\datashader\core.py", line 410, in bypixel
    dshape = dshape_from_pandas(src)
  File "C:\Users\user\AppData\Local\Continuum\Anaconda3\envs\TrendingAnalysis_GUI_python352\lib\site-packages\datashader\utils.py", line 344, in dshape_from_pandas
    for k in df.columns])
  File "C:\Users\user\AppData\Local\Continuum\Anaconda3\envs\TrendingAnalysis_GUI_python352\lib\site-packages\datashader\utils.py", line 344, in <listcomp>
    for k in df.columns])
  File "C:\Users\user\AppData\Local\Continuum\Anaconda3\envs\TrendingAnalysis_GUI_python352\lib\site-packages\datashader\utils.py", line 334, in dshape_from_pandas_helper
    dshape = datashape.CType.from_numpy_dtype(col.dtype)
  File "C:\Users\user\AppData\Local\Continuum\Anaconda3\envs\TrendingAnalysis_GUI_python352\lib\site-packages\datashape\coretypes.py", line 781, in from_numpy_dtype
    if np.issubdtype(dt, np.datetime64):
  File "C:\Users\user\AppData\Local\Continuum\Anaconda3\envs\TrendingAnalysis_GUI_python352\lib\site-packages\numpy\core\numerictypes.py", line 755, in issubdtype
    return issubclass(dtype(arg1).type, arg2)
TypeError: data type not understood

What it looks like as I step through all of this is that it can't recognize the datatype of the pandas data series??? Any help would be appreciated, hopefully in the form of a work-around that is viable for both 3.5 and 3.6 Python environments.

Relevant Environment: Python 3.5.2 DataShader 0.6.2dev3