Here's my rant explaining this:
Say the sentence out loud -- if you listen closely, your tongue naturally rolls off the 'l' because of the vowel length before it. This is what creates that illusion of a 'g' or fake vowel sound being tagged on the end.
Additional fun fact:
If your tongue didn't roll on its own, it's likely that your 'u' vowel length wasn't long enough, and you probably just said 'full/drunk' instead of 'ful/ugly'. :)