trunk: converting filtered shape to path removes filter effect (rev >= 13299)

With current trunk, converting a filtered (e.g. blurred) object to path removes the filter effect unexpectedly.

Steps to reproduce:
1) launch current trunk (default prefs, default new doc, locale: en_US)
2) draw a rect
3) blur it (or apply a predefined filter effect)
4) apply menu 'Path > Object to Path'

Expected result:
The shape (e.g. rectangle) is converted to path, keeping the filter effect (appearance unchanged).

Actual result:
The object is converted to path and the filter effect gets removed (appearance changes).

Based on tests with archived builds on OS X 10.7.5:
- not reproduced with stable 0.48.4, 0.48.5
- not reproduced with 0.48+devel rev <= 13297
- reproduced with 0.48+devel rev >= 13299
this regression seems related to the style refactoring committed in rev 13298/13299:
<http://bazaar.launchpad.net/~inkscape.dev/inkscape/trunk/changes/13299>

Reproduced with Inkscape 0.48+devel r13466 on OS X 10.7.5.