Video and Audio appear out of sync when they are not

Ok ok... I know the title probably has you wondering "what the heck is this guy talking about?". I literally just started using Windows Live Movie Maker to make lyric videos for some of my favorite songs that I just couldn't find one for on the internet. Pretty basic stuff... I add a background photo and then add the music file. I change the duration on the background to fit the audio. Now I have to add caption at just the right time so that the onscreen lyrics match up with the audio right? So I add a line of lyrics and adjust the start time and duration accordingly and on to the next line of lyrics. But I have found out that as I am going along and have to make multiple minor adjustments to a single line of caption... if I then drag the bar back just, lets say, 10 seconds so I can see if the caption (lyrics) are in sync with the audio... all of a sudden the audio and video appear to be out of sync. But if I start the project video from the beginning... it's actually not out of sync. This is a huge pain in the rear because everytime I add a single caption or line of lyrics... I have to start the whole video from the beginning to see if the timing is right and if it is not then I make a minor change in start time or duration of the caption then have to start the video completely over again. You can imagine how annoying this is when working with caption or lyrics towards the end of the song as it can take 10-15 mins per line of lyrics. 

I don't know if I am doing something wrong when "rewinding" a few seconds? I have tried to drag the bar back a bit and click play... same issue. I have tried just a simple click of the previous caption dialogue box to select that point and click play... same issue. I have also tried a simple click of the previous background frame but still have the same issue. 

Am I doing something wrong? Is this just a bug? Someone please help me understand this!

Thanks for any advice or tips in advance!