Your guesses are right, rush writs don't start until 20. It was the normal ones, and at the low level you can only get a level 15 writ until level 20, so even at 18 I'm making blue items from a level 15 writ. Also, the potion is one of the generic "from the store" ones and does indeed cover all forms of XP earning, including crafting. Nonetheless, even if the potion were not working, earning 5XP for a combine and 40ish for a quest makes NO sense when you have to earn 3800XP for the next level. I hope Bekkr's right and it was broken; I'm about to log in and try again. *edit* And I can confirm that Bekkr was right, and I'm now getting (with the various bonuses deducted out) 45XP for each blue combine, and ~675XP for the writ. Thanks, folks! Looks like it was a bug that has now been squished.