Question on memory allocation

Can someone explain why memory does not get released
for b in example below.

Rem
Release removes the internal reference caused by creating an integer handle to a type.
End Rem

Type MyType
field bigmap[1024*1024]
End Type

a=new MyType
Print MemAlloced()

release a
FlushMem
Print MemAlloced()
Print a

b:MyType=new MyType
Print MemAlloced()

release b
FlushMem
Print MemAlloced()

output:
Executing:Release.exe
4207424
8932
0
4203367
4203272