Gameplay bug with Skirmisher true damage

The new jungle item Skirmisher's Sabre applies true damage on hit after smiting the target. A friend and myself tested it in a custom game and the true damage dealt is less than the tooltip lists.

We tested different levels values and found that the true damage at level 1 should be 18, however only 17 was dealt. The following levels that were tested was: Level 5, intended damage - 30 damage dealt - 25 Level 6, intended damage - 33 damage dealt - 27 Level 7, intended damage 36 damage dealt- 29 Level 8, intended damage 39 damage dealt- 31

It seems that the true damage dealt is the tooltips listed damage subtracted by your levels numerical value.

It was tested in a custom game on the summoner rift beta map on different champions. We did not enchant the item.