Drop Shadow (and other filters) clips off shadow

Thanks for filling in a new bug report ! please

• Describe what you did (how to reproduce the problem, in details, with version 1.0-alpha or newer)

1. Start with a new Inkscape file.
2. Add a rectangle, and select it.
3. Choose Filters > Shadows & Glows > Drop Shadow
4. Turn on "live preview".
5. If clipping problem isn't shown, turn up blur radius.

• Describe what happened Drop shadow is added but clipped incorrectly.
• Describe what should have happened Drop shadow should not be clipped off
• Which exact version ? (run inkscape -V or look in Help→About Inkscape, top right) 1.0alpha