void* pointers get corrupted: D bug or misunderstanding?

[Dennis]

On Sunday, 28 July 2019 at 18:32:24 UTC, Federico Santamorena 
wrote:
> So the problem I am noticing is very simple: as you may know 
> GTK callbacks have a void* user_data argument, what happens, is 
> that if the flow of code is this: D => C => D the void* pointer 
> when reaching the third step and finally emerging to the D 
> language will change its value and get corrupted.

Can you give your exact callback function definition? I once had 
my context pointer corrupted because I marked my callback 
extern(C) instead of extern(Windows). Maybe you also have an 
error in your definition somewhere.