It amazes me how people can take one thing out of context and miss the point completely:
ROTJ
LUKE: "Leia... do you remember your mother? Your real mother?"
LEIA: "Just a little bit. She died when I was very young."
LUKE: "What do you remember?"
LEIA: "Just...images, really. Feelings."
LUKE: "Tell me."
LEIA: "She was very beautiful. Kind, but...sad. Why are you asking me all this?"
---
LEIA: "Luke, don't talk that way. You have a power I--I don't understand and could never have."
LUKE: "You're wrong, Leia. You have that power too."
---
LUKE: "Yes. It's you Leia."
LEIA: "I know. Somehow...I've always known."
So, first things first - Luke is definitely asking Leia about her real mother (Padmé) in ROTJ.
Now, in ROTS
Padmé dies when Leia is very young.
Padmé is certainly beautiful and kind, and by the end of ROTS has much to be sad about.
And it is established, later to be reiterated in the OT, that the Force runs strong in the Skywalker family.
Look at the greater context of that scene in ROTJ - what is it about?
One of the things it addresses is that very aspect of the Skywalker family - the Force runs strong in that family. The family is important.
Leia has these images and feelings regarding her mother.
She also somehow always felt that Luke was her brother - SOMEHOW she's always known.
It is just to show that Leia is blessed by the Force too, it isn't a big thing.
Leia is the missing part of the puzzle.
What Luke doesn't have (memories of his biological mother) Leia has.
What is going to get Luke to do what he has to do and redeem his father?
His love for his sister - we see it on the Death Star.
Everything is there - nothing contradicts anything.
The facts match up.
You accept that people can move things around with telekinesis.
You accept that people can generate lethal electricity with their fingertips.
You accept that people can leap hundreds of feet in the air from a standstill.
You accept that people can detect suffering and pain across the other side of the galaxy; see into the future.
Yet you cannot accept that Leia - who is strong with the Force - SOMEHOW has a residual image of her mother.
A mother who dies uttering the words "There's still good in him."
The Force must be brought into balance - only Anakin can do this.
He must be redeemed.
This is Padmé's last meassage - it is all part of that same puzzle.
The will of the Force.
Leia has her part.
Luke has his.
They have to work together.
Everyone has to work together, everyone has a different part of the puzzle.
So Leia remembers (although "remembers" is a misleading word to use) her mother.
Luke does not.
Big deal.
It all makes sense when you look at the bigger picture.
If you want to continue to look for contradictions, then you will definitely see them.
But the answers are there.