jdk1.2.2: Memory Leak in JInternalFrame

Using dispose() for a JInternalFrame finalize() is never called and memory is never released.
It is not possible to use the application because it hangs the client after opening and disposeing 3 or 4 big frames.
Customer configuration: WindowsNT4.0 SP3 + 32MB +jdk1.2.2

Tested and verified with:
a) Solaris7:
Solaris VM (build Solaris_JDK_1.2.1_03, native threads, sunwjit)
Patch: 106980-04 Obsoletes: Requires: Incompatibles: Packages: SUNWcsl, SUNWcslx, SUNWhea
Patch: 107078-10 Obsoletes: Requires: Incompatibles: Packages: SUNWxwfnt SUNWxwpl

b) WindowsNT4.0 SP3:
Classic VM (build JDK-1.2.2-W, native threads, symcjit)

Test code in attachment