I've tried to add subtitles to a DVDR.

First, I wanted to sync the subtitles, if theres any need for that, to the main movie.
What I did is ripping the main movie using DVD Decrypter (I've checked "Direct stream copy" and no for "File splitting").

Now, I've used Subtitles Workshop to sync the subs. Since the file I've ripped is identical to the source, I've assumed the subtitles I've synced will fit and no sync issues will come up.
But, as you most already figured, after demuxing and muxing with new subtitles (using DVD-Lab Pro), the subtitles went out of sync (2 secs approx. before video at movie's start till 5 secs approx. at movie's end.).

Is someone know why for that kind of thing to happen?

Thanks