If you use filter>blurs>blur...you can't change your mind, not in the obvious way by going back in and altering the value. If you set an object's blur then go back in the new values (which default to whatever was last used so not necessarily those used in the object) add to the current blur e.g. was 10 change to 12 makes it 22. I'd have thought it should bring up the current object blur values not the last used and then replace the blur using the new values.
You could use the filter editor but the dialog should work too or at least not work in a weird way.
Beyond the Basics Filters Blur "problem"
Inkscape.org
If you use filter>blurs>blur...you can't change your mind, not in the obvious way by going back in and altering the value. If you set an object's blur then go back in the new values (which default to whatever was last used so not necessarily those used in the object) add to the current blur e.g. was 10 change to 12 makes it 22. I'd have thought it should bring up the current object blur values not the last used and then replace the blur using the new values.
You could use the filter editor but the dialog should work too or at least not work in a weird way.