plotly.py: iplot doesn't display the graph at first in a new browser

hi, I use Plotly with Jupyter Notebook and it seems that the function to call ipilot in offline mode doesn’t always show the graph.

for example:

import plotly
import plotly.graph_objs as go
plotly.offline.init_notebook_mode()

trace = go.Bar(x=[2, 4, 6], y= [10, 12, 15])
data = [trace]
layout = go.Layout(title='A Simple Plot', width=800, height=640)
fig = go.Figure(data=data, layout=layout)

plotly.offline.iplot(fig)

after accessing the Jupyter Notebook online, when I first go in the notebook with the preview’s code, it will not show the graph, I’ll need to refresh the tab of the notebook after some time to see it.

there is no error in the console nor anywhere.

plotly version : 1.12.0 python version : 3.4.3 IPython version : 4.2.0

Kevin.