Photoshop Beta suddenly refuses to 'access' full 256 colour range when exporting to gif

Hi all, 

Recently, my Photoshop Beta has defaulted to only using 35 colours with a gif export (save for web) no matter how many times I select 256 colours and the Perceptual option.

Below you can see my settings and the massive colour shift from blue to green.

Also, the colours that are in the Color Table are all marked with a dot (what does the dot mean?) whereas previously 256 colours would have been used and only some had the dot on the swatch. Please help...