Error messages in stdout mess up piping output (import/export)

This bug has been fixed and closed but now it has resurfaced in 1.0.1 in Debian unstable.

https://bugs.launchpad.net/inkscape/+bug/171016

The command below

inkscape --export-type=png -p < a.svg > a.png

produces

• lots of stuff in stderr: Cool
• lots of lines before the PNG header: Not cool

The lines are of the form:

• WARNING: Requested update while update in progress, counter = 5 (repeated 3064 times)
• 96dpi (repeated 84 times)

I think this printouts shouldn't go to stdout. That breaks the output files on stdout

I can provide the a.svg if required.

• Inkscape Version: Inkscape 1.0 (4035a4fb, 2020-05-01) Pango version: 1.44.7
• Operating System: Debian
• Operating System version: Unstable