Manual Glow filter Vs Run-time GlowFilter?

Has anyone else noticed differences between glow filters applied manually and those applied using the GlowFilter class in actionscript?

If I create a simple white rectangle movieclip, and apply a glow filter to it with these properties:

blur x: 76
blur y: 79
Strength: 190%
Quality: High
Colour: White

I get a nice hazy glow around the rectangle.

If I do the same thing to the same movieclip like this:

[AS]
var glow_filter:GlowFilter = new GlowFilter(0xFFFFFF, 100, 76, 79, 190, 3, false, false);
glow_mc.filters = [glow_filter];
[/AS]

It’s a ridiculous white mess. It’s not glowing at all, it’s just a white blob. I’m kind of hoping I’m doing something wrong, but I cant see what it is. Any ideas?