When you type a word followed by a comma in the Meta Tags/Keywords box on the Site Outline, Sandvox automatically creates a 'blue bubble' for each word(s).

For example:
sandvox, howto, how to, step-by-step, tutorials, screencasts, problems
...becomes:

When published, this becomes:
<meta name="keywords" content="sandvox, howto, how to, step-by-step, tutorials, screencasts, problems" />
Note: the space after each comma.

To NOT have the space after the comma, use:
Site > [Site or Page] Code Injection... > Head Area > [Top Box]

...and inserting the HTML code:
<meta name="keywords" content="sandvox,howto,how to,step-by-step,tutorials,problems" />

...and leave the Meta Tags/Keywords box, empty.