Symbols are incorrectly cropped in map canvas if rotated

[Alister]

For a point layer, if I use a rectangle "simple symbol", and specify a rotation, the symbol is rotated in the map canvas, but it also has the corners cut off as if it has been cropped to fit in the area that it would have occupied if it was not rotated.

See attached screenshot (with a symbol dimension of 5m).

This problem does not seem to affect the composer, but note that it has its own bug with rotated symbols (#3778).