text valign: 'middle' not properly vertically centered

[nickolasreynolds]

Text rendering doesn't seem to calculate valign: 'middle' correctly. For large text regions it doesn't always stand out, but I'm still having to manually adjust rendering coordinates for text all over my layouts to deal with this issue. Here's an example of the typically erroneous behavior:

https://i.imgur.com/R1GddTC.png

The black-and-white dashed lines at the top and bottom of the image are the boundaries of the box in which the text should be vertically centered.