I am able to reproduce a sympathetic highlighting bug in which the entire resource is highlighted when you only want to highlight a small portion. Although it happens other times, here is how I can consistently make it happen:
1. Open NASB and NA27 Greek New Testament with sympathetic highlighting on.
2. Select words in the English text that includes a portion of 2 verses (it is important to cross the verse boundary). The appropriate words are highlighted in the Greek text,
3. Click in the NA27 window above the highlighted text and drag to highlight a word. The entire Greek text from the top to the word you selected on is now highlighted.

Sometimes the entire resource be highlighted at other times, even when I only select a word rather than parts of 2 verses. But I cannot make it happen as consistently as I can by following these steps. I am still trying to find the pattern that makes it happen other times. Hopefully this is reproducible enough that the bug can be located.