I always had this problem with kingdom hearts 1 and i don't know why I remembered it but ehh. Anyway when you return to traverse town in KH1 Riku takes Sora's keyblade and it doesn't vanish and return to Sora like it should've(I never understood that). But then when you reach Hollow Bastion the keyblade leaves Sora for Riku, but then later return to Sora blah blah blah. Anyway my problem is that when they met in Traverse town how could they both wield it? I mean the keyblade was meant for Riku so when he threw it back at Sora shouldn't it have returned to him? The only reason I could think of as to why it stuck with Sora was because his heart was stronger at the time, but then why didn't it return to him when Riku had it? So am I just over thinking this and missing the obvious reason or...?

They can both use it, so it wouldn't have returned to either of them without an express command. And Riku took it by force in Hollow Bastion because he was more powerful at the time.

At Hallow Bastion, Riku was more powerful and knew of the Keyblade's strength and abilities. He knew he could take it by force from Sora, if he wanted to, and as he was the more powerful of the two, Sora could not call it back.

In Traverse Town, Sora and Riku's power was either about the same or Sora was stronger. Riku was able to hold it for some time, because of his ability to wield the keyblade and Sora did not know he could call it back with his will.

The reason why Riku was able to weild the keyblade at Traverse Town was because he was origionally the owner of the Kingdom Key thanks to the fact that Terra performed the ceremony on Riku 10 years ago. Now when the keyblade went to Riku instead of Sora in Hollow Bastion it was mainly because his heart was stronger than Sora's at that point. But when the keyblade came back to Sora after the whole "My friends are my power" speech than it was because his heart became stronger than Riku's and that the keyblade accepted him as a true keyblade master. Now, the reason why the keybladestuck with him in the first place was mainly because he held Ven's heart inside of him. That allowed Sora to weild the keyblade in the first place. That, and the fact that Riku succumbed to darkness since he was origionally the owner of Sora's keyblade.

Yeah, Riku was a dick in KH1.

But yeah, since Riku is a Keyblade wielder also, he could hold Sora's Keyblade.

And Since in Hollow Bastion Riku's heart had been enforced by Darkness, he took Sora's Keyblade, and Sora's Keyblade went back to him after he realized his heart's true power.

Another thing is in Traverse Town, Riku didn't know that the Keyblade was suppose to go to him, therefore didn't try to keep it. While he would have remembered his encounter with Terra, Terra was rather cryptic and memory is only so good from 5 years old.