pycairo becomes slower with each call to show_text

Question

I am rendering to a cairo.ImageSurface using pycairo, version 1.23.0. I display the bitmap using pygame. Most drawing operations as would be expected take a constant amount of time + noise. However cairo.Context.show_text() keeps increasing in time with each call. In particular on frame numbers which seem to somewhat correlate with powers of two, the time taken is excessive. Thus I suspect that something weird with memory management/internal data structures is going on. I have included a basic working example below.

Am I doing something wrong? I know that it's the "toy" font API, but including pango or similar would be overkill for the application.

import pygame
import cairo
import numpy as np
from time import perf_counter


pygame.init()
screen = pygame.display.set_mode((1280, 720), pygame.SCALED, vsync=1)

while True:
    img_surf = cairo.ImageSurface(cairo.FORMAT_ARGB32, 1280, 720)
    ctx = cairo.Context(img_surf)
    ctx.set_source_rgb(.7, .7, .7)
    ctx.paint()

    start = perf_counter()
    ctx.set_source_rgb(.0, .0, .0)
    ctx.set_font_size(30)
    ctx.move_to(20, 50)
    ctx.show_text("Not very fast")
    stop = perf_counter()

    print(f"{stop - start:.07f}")

    img_surf.flush()

    result = np.copy(np.asarray(img_surf.get_data()))
    result = result.reshape((720, 1280, 4))[..., :3][..., ::-1]

    surface = pygame.surfarray.make_surface(np.transpose(result, (1, 0, 2)))
    screen.blit(surface, (0, 0))
    img_surf.finish()

    pygame.display.flip()

    list(pygame.event.get())