I think this is general error but it is most easily demonstrated with OK list.
Open a new empty list and and float Roster Statistics. Take a unit of Ironguts and all your percatages remain at 0%. Check the 'Gutlord' (Champion) for the unit and the core percentage jumps to 87.8%. Now, uncheck the very same Gutlord from the unit and your core percentage should go over 100%.
Selecting and unselecting champion seems to have very weird effects on the percentages in Roster Statistics.
Open a new empty list and and float Roster Statistics. Take a unit of Ironguts and all your percatages remain at 0%. Check the 'Gutlord' (Champion) for the unit and the core percentage jumps to 87.8%. Now, uncheck the very same Gutlord from the unit and your core percentage should go over 100%.
Selecting and unselecting champion seems to have very weird effects on the percentages in Roster Statistics.