This is normal. When you use FAST mode, it is assumed that you want to start the song immediately. The SD1 'skips' the intro parts of the midifile (where all settings for lyrics format, effect changes etc are stored). This is usually within the first 4-8 bars. Because they are skipped, when the song starts, the SD1 is trying to 'catch up' so the delay in lyrics being scrolled.
When you use NORMAL mode, all the information before the midifile is played is read and interpreted so the file plays correctly. We assume that when you use fast, you just want quick access to the song (quick start) and when you use Normal, you do not mind waiting a little for the parameters to load. This is the only way to get the song to start FAST. If we read all lyrics, effects ect parameters before starting the song, Song Fast will be the same as Normal since time is needed to read these parts.
Hope you understand why this cannot be changed.