I'm also using version 1.2 (Mac OS 10.6.8)and am seeing a large gap between the thumbs (displayed on top) and the main image.  It is especially large in Safari (v5.1.7)... it is better in Firefox (v16.0.2), but the gap is still quite large compared with what is shown the Juicebox builder.  The gap is significant enough (especially in Safari) to definitely be defined as a problem. 

Main image settings:
padding 0
Frame Width 0
Image shadow Blur 0

Thumbnail settings:
Thumb Position: Top
Show large thumbs is checked (only box checked)
Max Thumb Columns: 9
Max Thumb Rows:  1
Thumb Padding: 3

Button Bar Settings:
Button Bar Position: Top
Button Bar HAlign: Right
Nothing is checked