Matplotlib: Non-uniform fonts in .pdf after changing from Type 3 Font to Type 1 Font

I was asked to change some figures in my paper from using Type 3 Font to using Type 1 Font, and I found the instruction to do just the job.

By adding the following 3 lines, I am able to generate a Type 1 Font .pdf file:

matplotlib.rcParams['ps.useafm'] = True
matplotlib.rcParams['pdf.use14corefonts'] = True
matplotlib.rcParams['text.usetex'] = True

However, while the font of x-tick and y-tick on my old plot were uniform, their fonts somehow became different after I added the 3 lines of code. This seems strange to me since the change is applied to only one of the ticks.

Here is the script in python:

import matplotlib
matplotlib.use('PDF')
import matplotlib.pyplot as plt
from matplotlib.backends.backend_pdf import PdfPages


# Switch to Type 1 Fonts. 
matplotlib.rcParams['ps.useafm'] = True
matplotlib.rcParams['pdf.use14corefonts'] = True
matplotlib.rcParams['text.usetex'] = True


def plot_pdf_figure(path, title, xl, yl, xt_list, yl_list, style_list):
    fig = plt.figure(path) 

    ax = fig.add_subplot(111)
    ax.set_title(title)
    ax.set_xlabel(xl, style='italic')
    ax.set_ylabel(yl)

    x_list = range(0, len(xt_list))
    plt.xticks(x_list, xt_list)
    for y_list, style in zip(yl_list, style_list):
        ax.plot(x_list, y_list, style)

    pp = PdfPages(path)
    pp.savefig(fig)
    pp.close()



plot_pdf_figure("test_plot.pdf", "test", "x-axis", "y-axis", [1,2,3,4,5,6], [[1,2,4,8,16,32],[32,16,8,4,2,1]], ["-ro","-gs"])

Thank you for any guidance or help!