The adventures of Foo

Can someone explain me the following behaviour:

I have the following smart pointer:

class AlsaHwParams
{
public:
AlsaHwParams() : m_params(0)
{ snd_pcm_hw_params_alloca (&m_params); }
 
~AlsaHwParams()
{ if (m_params != 0) snd_pcm_hw_params_free (m_params); }
 
operator snd_pcm_hw_params_t*() { return m_params; }
private:
snd_pcm_hw_params_t [...]