Thought everyone would be interested in this patent. It mentions a lot of the reasons for using a ceramic insert in the piston.
I could also see that using a modified brake pad could cause uneven pressure on the piston insert and cause the disintegration.
2014 X3 28i xDrive - Jet Black, Black Leather, Cold Weather, Driver Assistance
(On order) 2017 M240i - Mineral Grey, Terra Leather, Cold Weather, Driver Assistance, Nav, 6MT