It's a design feature of Tesseract. https://github.com/tesseract-ocr/tesseract/issues/1769 As most PDF viewers display transparently bitmap data under the GlyphLessFont -> the solution would be rather to fix the bug in Evince.
As php7 arrived, the current codebase is no longer working. Are there any plans to continue development of Wiki Web Help in future ? Kind regards, Marek