Removing black edge around white outer glow

[Aaron244833139eh1]

Hi all. 

Working in CS6 (on an old Mac), and I can't work out if what's going on here is a bug, or I've messed up. Had a white outer glow applied to some text, have screenshotted the parametres below. Got asked to make the image larger, and when I increased it from 300 px/inch to 300 px/cm, the outer glow suddenly got a black border outside of it. Tried removing the layer style and re-applying it after enlarging, and the same thing happens. Any explanation of what's happened here, and of how to get rid of it? Have added before and after pics. 

Before (what I want)

After (what I don't want)

Parametres of the outer glow

[melissapiccone]

Did you redo the outer glow with new settings? It usually doesn't look right when you resize and you have to redo the layer styles. 

[j.krueger]

Make sure to check that scale styles is turned on in the image resizing.