Bug concerning PDF "Optional Content" feature...

[Édouard Canot]

Hi,

The attached PDF file, "Labels_and_Languages_3_OC.pdf", clearly reveals 
a bug in okular: some graphic objects are not erased when switching 
between mutually exclusive Optional Contents (implemented via the 
RadioButton group).

This PDF demonstrates the "Optional Content" feature... When opening it 
with any browser, you can open the layers and choose one language among 
three available ones (there are mutually exclusive). Most of PDF 
browsers (Adobe Acrobat Reader under Windows, Evince under linux, ...) 
behave well. The problem comes when using okular: when switching from 
one language to another, the old active PDF object is not erased, and 
all texts are overwritten on the display.

This bug appeared for me since Ubuntu-17.10 (therefore for 
okular-1.1.3). Previously (under Ubuntu-17.04, okular-1.0.3), it was 
correct. The bug is still present in okular-1.6.3 under Ubuntu-19.04.

The PDF has been generated by my own graphic library Muesli. You can 
open it with any text editor since it uses only ASCII characters. To my 
knowledge, it is standard compliant: 'mupdf' doesn't claim about any 
errors, and the "PDF Tools Online" validator 
(https://www.pdf-online.com/osa/validate.aspx) returns nothing special 
about it:
/Validating file "Labels_and_Languages_3_OC.pdf" for conformance level 
pdf1.5//
//    The document does conform to the PDF 1.5 standard.//
//    Done./

Regards,
Édouard Canot

-- 
Édouard Canot
tél: +33 (0)2 23 23 53 77
Institut de Physique de Rennes
CNRS, Université de Rennes
Bât. 11A, bureau 129
Campus de Beaulieu, F-35000 Rennes
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