Oh my. I’ve started using Inkscape to review some lecture’s notes and I soon hit Inkscape Bug #485269 – Strange Black Boxes
Those black boxes pop up and do not go away. Learn to make them disappear.
Text become black boxes. As a temporary workaround I exported it as PNG. But that’s annoying, expecially when you read Inkscape FAQ reporting:
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).
Oh my! It’s still there after SIX years.