Fix z-index switching when element is deselected

[timseverien]

Reproduce

1. Have two tags sit near each other
2. Activate one
3. Quickly activate the other
4. Quickly move mouse to another position, deactivating all

The z-index works just fine, but when all tags are deselected, the z-index is reset, causing the z-order of elements to respect DOM-order, in turn possibly causing flickering.

Solution

Make sure the z-index sticks until the element is hidden.