app.diagrams.net SVG export can create files with incorrect text

[slawr]

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Describe the bug
Exporting the same diagram as editable SVG sometimes results in files with text that is incorrectly rendered when consumed in various downstream apps including browsers (Firefox, Edge) and desktop applications (e.g. Powerpoint).

In the cases when the export result is incorrect the file size is much smaller than the correct case.

To Reproduce
This has been an annoying issue for many months that I may have finally isolated.

Steps to reproduce the behavior:

1. Go to app.diagrams.net and draw a diagram with default (built-in) font styles
2. Export an editable SVG with the following settings:
   
   Does not seem to matter if you save a local or google drive file.
3. File is saved, but when opened the text is either not visible (e.g. Google drive preview) or rendered incorrectly (e.g. Powerpoint reports Text as not being SVG). File size is small, e.g. 20KBytes.
4. Export again using same settings, but clear embed fonts checkbox and reselect it.
5. Saved file is now much larger, e.g. 300KBytes and renders correctly. I've not debugged the XML but I guess the difference is the embedded font and that perhaps the embed font checkbox is sometimes not being honored. See good and bad export examples below.

Expected behavior
Consistent editable SVG file with embedded text and font

Screenshots
Example of exported diagram file that renders incorrectly:
BAD-CDSP-C4-Model-L1-System-Context-diagram drawio

Example of exported diagram file that renders correctly:
GOOD-CDSP-C4-Model-L1-System-Context-diagram drawio

Both files were created from the same diagram one after the other in the same session in the sequence above.

draw.io version (In the Help->About menu of the draw.io editor):

• draw.io version v24.8.6

Desktop (please complete the following information):

• OS: Win 10
• Browser Firefox
• Browser Version 130.0

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

I tested the problem in incognito/private mode with all browser extensions switched off, write "yes" below:

• yes

Additional context
Add any other context about the problem here.