I like to make solid bar plots without lines around each bar, eg:

plt.hist(data,fc="gray",lw=0.0,alpha=0.5)

Problem: the first bar does not exactly line up with the other bars. There is a slight misalignment visible on the right and bottom edges. Depending on the window size this shows either as a white gap or a darker overlap (visible because alpha=0.5).

The other bars are all properly lined up.

Confirmed both in the notebook inline mode and the QT backend on OSX.
matplotlib.__version__ = '1.4.3'

Steps to reproduce:

importmatplotlib.pylabaspltimportnumpyasnpplt.figure()plt.hist(np.random.uniform(0.0,1.0,size=1000),fc="gray",lw=0.0,alpha=0.5)plt.show()

Then resize the window and observe.