filter parameters changing

[Saka Nakai]

On:
- Inkscape 0.48.2 r9819
- Windows Vista Dutch
- Inkscape Interface: system default (and thus dutch)

#1 My first encounter
Problem: after changing the "Lichtbron" (light-source) parameter of the "Lichtbron" (specular) filter the filter doesn't work properly anymore. After selecting another filter (see procedure below) it then select the "Lichtbron" filter again, the "Lichtbron" parameter is changed (eg to distant, although I selected 'point' at first).

I changed the interface language to English and the problem disappeared.

One way to generate the problem:
- new document
- create a rectangle
- add the filter: Filters -> Verhogingen -> Gecombineerde verlichting
- open filter editor
- (enlarge filter area such that you can see all 7 filters)
- select "Lichtbron" (5th filter)
- change parameter "Lichtbron" from "Puntlicht" to "Veraf licht"
- select another filter (eg #1: "gaussiaans vervagen")
- don't change anything
- select #5 "Lichtbron" again

==> the parameter "Lichtbron" has changed back to "Puntlicht" AND the filter doesn't work accordingly to the parameter settings

#2 After playing around a bit with the filters I found that the problem is much bigger then on the one filter as described. With similar procedures you will find quickly that the other lighting (diffuse) has the same kind of problem. Furthermore changing the light source not only can change the parameter values, it even can change the parameter set. This you can reproduce like this:
- in the above example
- select lightsource
- select "Puntlicht"
- select "Spotlicht"
  => now you see the "Puntlicht" parameter set
- select "Veraf licht"
- select "Spotlicht"
=> now you see the proper "Spotlicht" parameter set

[su_v (suv-lp)]

Likely related to similar issues with the filter editor dialog:
Bug #194408 “Filters don't always use parameters as displayed in dialog.”
Bug #216945 “Filter Effects - editing text control problem”
Bug #462748 “Filter editor dialog display size incorrect”
Bug #386627 “Data display remanence in filters Color matrix dialog”