All users can choose deactivated styles.

An example of this on a stock installation of phpBB 3.0.9:

1. Login to the Administration Control Panel (ACP) and click the 'Styles' tab.
2. Install subsilver2 and deactivate it.
3. Go to User Control Panel > Board preferences > Edit global settings. Under 'My board style' notice only prosilver can be selected.
4. If using Google Chrome, you can right-click the style selection box and click 'Inspect Element'.
5. Expand the tree and you will see '<option value="1">prosilver</option>'.
5. Change the value (the style ID) to 2 and click 'Submit'.
6. You will now be using the subsilver2 style even though it is deactivated.

This can be problematic if a style is deactivated pending any edits for a modification. A deactivated style should only be accessed if previewing it via the ACP.