Small window width makes for ugly navigation.

[miekd]

The float doesn't fix and therefore the navigation bar items get pushed down.

Possible Solution no. 1; A min-width.

Possible Solution no. 2; Explore a media query that makes relative sizes of the buttons at a certain width.

Both are not optimal.

[PaulAdamDavis]

I would vote for a min-width of what the image being shown is. If the visual is not responsive, why should the UI of its parent?

[miekd]

Good one. I'll keep it in mind :)