Array deletion problem
First of all: it is not a good idea to do dynamic memory maagement in embedded systems (in casu arduino)
Secondly freeing memory means: marking the memory as available. It does not mean "setting the memory to 0"
because ar still points to the same locaton in memory it is "normal" that it also still reads the old values. Only -according to the C CP0P0 pàrogramming rules- you should not do so. Reading will not cause problems but writing will very likely.