Bug report

Bug summary

If Axes3d was repositioned by set_position() prior to figure size change, it will not adjust its size. Normal axes behave differently.

Code for reproduction

import matplotlib.pyplot as pl

def adjustPos(ax, shift=-0.08):
    pos = ax.get_position()
    ax.set_position(pos.translated(shift, 0))

#axes grid
N = 10
C = 2

fig = pl.figure() #default (small) size

fig2 = pl.figure()
fig2.set_size_inches(7,2*N)


def adjustPos(ax, shift=-0.08):
    pos = ax.get_position()
    ax.set_position(pos.translated(shift, 0))

for ii in range(N):
    #add and shift (by zero) normal and 3d axes
    ax = fig.add_subplot(N, C, 1+ii*C)
    adjustPos(ax, 0)
    
    ax = fig.add_subplot(N, C, 1+ii*C+1, projection="3d")
    adjustPos(ax, 0)

    #the same for already large fig2
    ax = fig2.add_subplot(N, C, 1+ii*C)
    adjustPos(ax, 0)
    
    ax = fig2.add_subplot(N, C, 1+ii*C+1, projection="3d")
    adjustPos(ax, 0)
    
fig.savefig("test_original_size.jpg", dpi=300)
fig.set_size_inches(7,2*N)
fig.savefig("test_large_size.jpg", dpi=300)

fig2.savefig("test_big_figure.jpg", dpi=300)

Actual outcome

If axes positions are adjusted by calling set_position(), even if the actual shift is 0, Axes3D will keep its size determined for the original size of figure.
Original figure size (axes do not fit comfortably):

Figure enlarged after axes are created and shifted:

This effect will not take place if set_position() is not called. The issue can be easily avoided by setting figure size ahead of axes creation as done with fig2:

However, I would expect this behaviour regardless of where the figure size is changed.

Matplotlib version

• Operating system: Debian GNU/Linux 10
• Matplotlib version (import matplotlib; print(matplotlib.__version__)): 3.4.2
• Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
• Python version: Python 3.7.3
• Other libraries: