QGIS » QGIS Application

After compiling QGIS 3.4.3 from sources, I can star it but the console logs the following (with many hundreds of the first 3 lines):

(...)
libpng warning: Application was compiled with png.h from libpng-1.6.34
libpng warning: Application  is  running with png.c from libpng-1.2.56
libpng error: Incompatible libpng version in application and library

If for example I try to open the Help windows, it crashes a few milliseconds after the pop-up with information about softwares' version appeared:

Reading contributors file /usr/local/share/qgis/doc/CONTRIBUTORS.............................................
libpng error: Libpng jmp_buf still allocated
QGIS died on signal 11Could not attach to process.  If your uid matches the uid of the target
process, check the setting of /proc/sys/kernel/yama/ptrace_scope, or try
again as the root user.  For more details, see /etc/sysctl.d/10-ptrace.conf
ptrace: Operation not permitted.
No thread selected
No stack.
gdb returned 0
Aborted (core dumped)

I'm on Ubuntu 18.04 (4.15.0-43-generic x86_64 GNU/Linux)

Note, apt-cache policy shows me:

$ sudo apt-cache policy libpng-dev
    libpng-dev:
        Installed: 1.6.34-1ubuntu0.18.04.1
        Candidate: 1.6.34-1ubuntu0.18.04.1

So I do not know from where it found libpng-1.2.56 in the messages above...