Was working with Inkscape and upon viewing the SVG file in an image viewer, I noticed conspicuous black boxes that were not present in the Inkscape view of the SVG or the exported PNG version of the SVG. A quick Google query turned up a standards conflict.
The Inkscape FAQ reports:
When flowed text support was added to Inkscape, it was conformant to the then-current unfinished draft of SVG 1.2 specification (and was always described as an experimental feature). Unfortunately, in further SVG 1.2 drafts, the W3C decided to change the way this feature is specified. Currently SVG 1.2 is still not finished, and as a result, very few SVG renderers currently implement either the old or the new syntax of SVG 1.2 flowed text. So, technically, Inkscape SVG files that use flowed text are not valid SVG 1.1, and usually cause problems (errors or just black boxes with no text).
I found out that it was the flowed text. Now to remove the flowed text. It did not seem to exist, though, making deleting the flowed text difficult. One could remove the visible text, but the black box would remain.
Another Google query turned up this Inkscape bug to which this simple workaround was suggested:
Another workaround to find empty ‘Flowed text’ objects:
1) ‘Edit > Deselect’
2) activate the text tool
3) use <TAB> to cycle through all text objects in the drawing and watch the status line for the message “Type or edit flowed text (0 characters); Enter to start new paragraph”
4) use <DEL> or <Backspace> to delete the selected empty ‘Flowed Text’ object
5) continue with until the first text object is selected again
I was unable to delete the boxes with Delete or Backspace. I settled with right-clicking on the box and deleting it that way. Save, then view the image again. The black boxes should be gone. To prevent them from returning, use the “Text > Convert to Text” tool to turn all flowed text into static text.