https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=802778
10 years old. It never was a false positive. It was fixed a good few years ago. The fix did not involve suppressing the error.
Valgrind does need a lot of work, especially for missing CPU features and for Darwin. I’m not aware of many memcheck bugs that aren’t relatively obscure corner cases.
If you have encountered bugs please report them to https://bugs.kde.org.