The IconButton does follow the default material specs and has a splash radius of about 24px. This is definitely not suitable for auto generated icons like the back button and the scaffold drawer button.

Though the material design does specify a set splash radius, an overflow is definitely not intended. The icon button's splash always overflows in AppBars.

Possible solutions -

1. Allow setting the default splash radius for all auto generated icon buttons in AppBars.

2. Set the default splash radius so that it doesnt overflow atleast - in the defaul AppBar