QString crash when moving across a plugin boundary

[Jakob]

Recently I noticed the following:

• In my application there is a 'core' bit, which has a certain function that accepts a const QString&, say f(const QString&) (it's actually a function that will popup a QFileDialog and the string is the caption)
• The application loads plugins, and the plugins get access to this function f
• Recently I was calling this function from within the plugin, without explicitly typing a QString, so I was calling f("File Dialog Caption") - in other words, I tried relying on implicit construction
• This caused a crash in the core part, where, as far as I could tell, the internal data of the QString object was pointing to NULL
• Then I changed the call by explicitly calling the QString constructor: f(QString("File Dialog Caption")), which resolved this crash

I'm (almost) sure this has something to do with the magic that happens when moving across dynamic libraries (this is on Windows, but I read that similar problems occur on *nix)

So, can someone explain (or refer to some clear explanation) about this magic? I have been googling quite a bit, but I find it hard to get details about what is happening. Then the obvious next question is, what is the connection with QString?