We perform some tests, and it seems to render as expected on our side. It would be valuable to us if you open new support ticket and send the problematic report with some test data in order to investigate further.
In general, the HTML5 rendering extension is based on the Image rendering extension, with some differences. We recommend referring to Design Considerations for HTML Rendering
help article, in which are listed all specifics to that exporting mechanism.
Consider that the strings are measured using GDI+. This can lead to differences between Image rendering and the Web Browsers.
Our recommendation is to use PDF rendering extension instead.
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