Move Glitch

I was playing a correspondence chess game against a friend of mine, and he came to me with his laptop, and he let me see a move that he made.  I saw him do "Bb6."  I told him, "I got your Queen," because he never realized that I discovered-attacked his Queen by moving my Pawn to attack his Bishop and support my Knight.  When I logged in to make my move, it was different than what I saw, and it put me in check.  I had no choice but to block it.  Since I told him that his Queen was in danger, he then moved it out of the way.  I was very confused as to why his Bishop was at a different spot than where it really was in.  The next day, he told me that he noticed the glitch as well.  Here is what happened:

It did not matter, but I am mainly worried that it will happen again, for or against me.  Is this a rare event, or does it happen from time to time, and can it be prevented?

Hmm... Normally when pieces are appearing in strange places on the board, or you notice that a move looks different from when it did originally, there is an issue with a cached page. From what I can see in the game that is what took place. Sorry for the confusion!

That makes sense; thank you for the answer!  Is there any way to correct a cached page or prevent the issue with the cached page from happening, even if it is my opponent's move?

uh, reload? That's what I do when I lag.

(Never in 1 min obviously)

Sure, I can refresh the page when it is my move (thank you!), but the trouble is that when I saw my opponent in the game above make Bb6, it stayed that way on his computer after he hit "submit move."  I logged on 30 minutes later to find Bb4+.  There was no lag on his computer, and the Bishop moved to a different (yet legal) place on my computer.  However, could it be possible that it was the computer that I was on that needed refreshing before I make my move, and would it place the Bishop back to Bb6?

We do suggest you clear your browsing cache occasionally. There are some instructions here http://support.chess.com/Troubleshooter/Step/View/2

If you let me know what browser and operating system you're using I can give more specific instructions :)

I use Google Chrome on a Windows Vista with a Windows 64-bit operating system.

On the right side of your address bar, click the chrome menu button 

Thank you for the instructions!  So, I just empty the cookies and cache before I make a move to ensure that my opponent's move was the one he/she made?

No, no need to do it that often. Just do it maybe once a week (when you're not in live chess) to try to keep things fresh :)

That looks good to me, thank you!