Okay, thanks, I see what you mean. I was probably testing using a modified version by mistake. Anyway, in PhpDig v.1.8.7, find the phpdigCleanHtml function in robot_functions.php, look for the following line, and try removing the dash in the character class.
Code:
$text = eregi_replace("[*{}()\"\r\n\t-]+"," ",$text);