Bug summary
The coordinates of text (legends, titles) are not properly set in pgf files.

Code for reproduction
Producing the pgf figure with a slightly altered pylab_examples "tex_demo.py":

import numpy as np
import matplotlib.pyplot as plt

plt.rc('text', usetex=True)
plt.rc('font', family='serif')
plt.figure(1, figsize=(6, 4))
ax = plt.axes([0.1, 0.1, 0.8, 0.7])
t = np.linspace(0.0, 1.0, 100)
s = np.cos(4 * np.pi * t) + 2
plt.plot(t, s)
plt.xlabel(r'\textbf{time (s)}')
plt.ylabel(r'\textit{voltage (mV)}', fontsize=16)
plt.title(r"\TeX\ is Number $\displaystyle\sum_{n=1}^\infty"
          r"\frac{-e^{i\pi}}{2^n}$!", fontsize=16, color='r')
plt.grid(True)
plt.savefig('tex_demo.pgf')    # altered line
plt.show()

Taking this pgf file ("tex_demo.pgf") in my latex file:

\documentclass{article}
\usepackage{pgf}
\begin{document}
\input{tex_demo.pgf}
\end{document}

Actual outcome
This gives the output "Bugreport.pdf".
Bugreport.pdf

Expected outcome
The graphic should look like in the example:
http://matplotlib.org/examples/pylab_examples/tex_demo.html

Matplotlib version

• Matplotlib 1.5.2rc2, Python 3.5.2 and Fedora 25 (Workstation Edition)
• All components were installed via the Fedora specific system tools (dnf) from Fedora repositories