The first is, annoyingly, a relatively common problem and solution when dealing with GC lifetimes in tests. Few interpreters/JITs want to generate extra instructions to null out stack slots or pre clobber registers to ensure something becomes collectible at a specific point. Eager nulling of a variable often gets removed by dead store elimination or even just from being a disconnected SSA node. I've written extra nested scopes or wrappers in Java to deal with this in tests.
Don't know anything about the second one.