Lines sometimes overlap when one wraps by a small amount

[csmith]

Expected Behavior

When adding lines to a vertical styled text area, none should overlap.

Actual Behavior

If two lines, A and B, are added sequentially, and A is very slightly too long to fit in one line, the wrapped part of A overlaps the start of B.

e.g.:

The first line almost fits in, but is a few pixels short. It wraps, but the height calculations don't seem to take notice of that and the second line renders on top of it.