Created attachment 186522 [details]
Test Plasma Style

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SUMMARY
The panel size in Plasma Styles now goes haywire whenever using Plasma Styles that have PNG embeds in their panel-background.svg, whom have the respective background part IDs assigned to themselves, such as with Fluffy Bunny and the attached test style.

STEPS TO REPRODUCE
1. Apply Fluffy Bunny or the attached test style
2. Replace plasmashell
3. Watch panel randomly become massive sizes such as 478px despite not needing to be

OBSERVED RESULT
The panel becomes way larger, in my tests consistently 478px, upon plasmashell launching even though it was a normal size, such as 40px, prior to the relaunch. Additionally, in some cases it refuses to be shrank lower than the enormously huge size, and in some cases also the panel toolbox toggle randomly spans the entire 'right' piece's size rather than being its usual size - it's all random-chance.

EXPECTED RESULT
As it was prior - panel does not decide it wants to be stupidly huge, and the toolbox toggle is always its usual size.

SOFTWARE/OS VERSIONS
Windows: 
macOS: 
(available in the Info Center app, or by running `kinfo` in a terminal window)
Linux/KDE Plasma: 
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION