In Lazarus 0.9.2 (i used before) MultiSelect work as Extendet select with Ctrl (add to selected) and Shift(range selected).
It work good.
In Lazarus 0.9.8 it not work. (work as select and deselect with always Ctrl pressed). Its not good.
I use Linux(Gtk1)
(Look like In GTK2 it work as in 0.9.2)