fix positioning on height and a proposal for changing the logic of positioning

When approaching the lower end of the container also appears bug in a tooltip.

Changing the position of a tooltips is better to apply after filling the contents and change its size. In addition, we do not need the extra steps to determine the position when a tooltip is hidden. Otherwise, we can observe twitching clue if we will have to appear scrollers in the container.
![bug1](https://f.cloud.github.com/assets/575826/559023/ca8f2528-c43c-11e2-8693-e650d3e73fdd.png)
![bug2](https://f.cloud.github.com/assets/575826/559024/ca9450f2-c43c-11e2-8265-b68ced5ed937.png)