Steps to reproduce:
1. Create a new Draw document
2. Create a new Style: right click to "Default", "New..."
3. The name of this Style is "Untitled1"
4. Go to Tab "Line", change the color to red, set width to 0.20cm, so the line is good visible
5. Press OK, there is now a new Style "Untitled1" in the Sidebar
6. Right click on "Untitled1", "New..."
7. The name of this Style is "Untitled2"
8. Go to tab "Area", set fill color to green
9. Press OK, there is now a Style "Untitled2" in the Sidebar, which is a Child of "Untitled1".
(The Properties Dialog shows Inherit from "Untitled1")
10. Create a Rectangle, Apply Style "Untitled2". The Rect gets a red border and green background.
11. Save the file as test.odg
12. Close Draw
13. Open draw again, open test.odg

Expected Result:
There is a green Rect with a red line.

Current Result:
The Rect has still a green background, but no red border anymore.
The Style "Untitled2" has no parent, (Inherit from "-None-"). It's in the same Position as "Default".


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Some interesting Details:
in styles.xml I found this entry:
<style:style style:name="Untitled2" style:family="graphic">
<style:graphic-properties draw:fill-color="#00ff00"/>
<style:paragraph-properties style:writing-mode="lr-tb"/>
</style:style>

How to fix it:
1. Drag & Drop the Style "Untitled2" to "Untitled1"
2. Save the file again

Look now at styles.xml:
<style:style style:name="Untitled2" style:family="graphic" style:parent-style-name="Untitled1">
<style:graphic-properties draw:fill-color="#00ff00"/>
<style:paragraph-properties style:writing-mode="lr-tb"/>
</style:style>
The Style is now Saved.