Occlumency and Shield Charm

[severelysigune]

No: HPFGUIDX 89368

I have been wondering lately about what happened in the one before 
last of Harry's Occlumency lessons. There, Harry casts a Shield Charm 
and the result is he gets to see some of Snape's memories. What I 
find strange is that something like a simple (?) Shield Charm should 
permit Harry to get inside Snape's mind. I think that is strangely in 
contradiction with the repeated qualification of Snape as a superb 
Occlumens.

Even if Harry's Shield Charm made Snape's spell bounce off and caused 
him to be hit by his own Legilimenting spell, it still seems to me 
that it should be a piece of cake for Lord Thingy (an expert 
Legilimens, better at it than Snape) to break into his sneaky ex-
servant's mind. So can Snape really rely on this Occlumency business? 
Or does anyone have an alternative explanation for what happened?


Yours severely,

Sigune