Extent of a basemap varies once it's been saved to disk

[darribas]

The extent of a basemap is changed

In [80]: pl = ctx.Place('boulder', zoom_adjust=-3, path='temp.tiff')

In [81]: pl.bbox_map
Out[81]: 
(-11740727.544603072,
 -11701591.786121061,
 4852834.0517692715,
 4891969.810251278)

In [82]: rio.open('temp.tiff').bounds
Out[82]: BoundingBox(left=-11740803.981631357, bottom=4852910.488797557, right=-11701668.223149346, top=4892046.247279563)

In [83]: rio.open('temp.tiff').bounds[0] == pl.bbox_map[0]
Out[83]: False

I'm not sure why this is happening but would be nice to at least know why. In principle, I'd expect both basemaps to have the same extent.