Reproduction steps:
1) Download and open attached project ("ABDemo.zip")
2) Build asset bundles (upper menu: AB\Build)
3) Open file explorer and go to .\Assetbundle\ab\mat\
-- Notice that ui.ab 's size is bigger than .\Assetbundle\ab\tex\ui.ab 's (which means ui.ab from mat folder contains texture and material)

4) Change Texture's type from Sprite to any other (for example Default)
5) Build asset bundles once again
-- Notice that ui.ab from "mat" folder size is much lower

Expected result:
Material's asset bundle should not contain texture itself

Regression appeared in 5.4.0f3

Reproduced with:
5.4.0f3, 5.4.5p1, 5.5.3p1, 5.6.0p2, 2017.1.0b1

Unable to reproduce:
5.3.8f1