The problematic and also enlightening passage for all theories about Pensieves is Snape's Occlumency lesson with Harry when Harry sees the memory of his father. Snape removed the memories he did not want Harry to see before the lesson.

Snape was standing with his back to Harry, removing, as usual, certain of his thoughts and placing them carefully in Dumbledores Pensieve. He dropped the last silvery strand into the stone basin and turned to face Harry. ...

[Harry] turned around. The light was coming from the Pensieve sitting on Snapeʹs desk. The silver‐white contents were ebbing and swirling within. Snapeʹs thoughts… things he did not want Harry to see if he broke through Snapeʹs defences accidentally…

So these memories that Snape put in his Pensieve can no longer be accessed through Legilimency. But still, when Snape surprises Harry watching his Pensieve memories, he clearly knows what they are about.

ʹAmusing man, your father, wasnʹt he?ʹ said Snape, shaking Harry so hard his glasses slipped down his nose.

ʹI ‐ didnʹt ‐ʹ

Snape threw Harry from him with all his might. Harry fell hard on to the dungeon floor.

ʹYou will not repeat what you saw to anybody!ʹ Snape bellowed.

To me that means that even when one put one's memories into a Pensieve, and even when they can no longer be detected by Legilimency, one still has them somehow in one's mind and can still remember them.

This!

I was just about to comment with this same passage. I think that it could also be dependent on your intention. If you remove the memories with the purpose they wouldn't be able to be accessed by legilimency, then that's how it works, but if you are using the pensieve in order to take a closer look (different perspective) at the memory, then it's like copying a segment, and the original is intact.

With Dumbledore's odd sayings "head too crowded," etc... I think he's being telling Harry what he's doing in an odd, old man exaggeration sort of way (watering it down to youths so they grasp a subject too complicated to really explain in a short time frame)

I'm not sure I'm making much sense, but this also brings to mind the Hall of Prophecy... those memories "are" copies and Dumbledore says as much. That despite the record being destroyed, the real memory still exists in the mind of the one who heard it in the first place.

That's the thing, I feel like there has been support for both the copy and original theories. Maybe, like you say, it's about intent. Perhaps there are two different spells depending on what the purpose of the memory "withdrawal" is...

I totally go for the theory that intention plays a big part in what happens with memories in a Pensieve. Rowling's magic has a lot to do with the will and intent of the wizard or witch doing the magic. #

And yes, I can see Dumbledore using "head too crowded" as a figure of speech to explain why he himself is watching his own memories in a Pensieve. What it means to me is that a Pensieve memory is different than your own memory in some ways - you get an outsider's fresh view on what happened, also perhaps there are things in your memory that you don't consciously remember but that are still there somehow (Muggle memory works like that too ;)).

Oh good point! Though it almost brings us back to square one, because these scenes definitely imply that both ideas are correct.

Though perhaps for pensieves, its the original memory that is removed and a copy left in it's place, making viewing the memory through legilimency impossible, but still creating an imprint for the remover to remember.

Not sure if that theory makes any sense.

I think what this scene implies is that memories and putting memories into Pensieves is a more complex affair than copying data on a computer. I am not sure one can distinguish between an "original" memory and a "copied" memory. It's the same thing as both are memories. What actually happened - that is the original.

I like Mab's intent theory. :)