I do not use KiCad often / dayly.
Last week I started a small project only just to draw a schematic with a few symbols and post it on a forum. (No intention of designing a PCB).
I edited a symbol in the library editor and when updating the graphichs in EEschem it seemed to take a bit longer than usual.
But it all worked, no real problems for me.
Some half bright light started to shine in the back of my head:
If your symbol is directly from github (yuch) or in a read-only place you have to copy it first to a library of your own before you edit it..
KiCad projet manager -> Help -> Copy Version Info:
Version: 4.0.7-e2-6376~58~ubuntu14.04.1 release build
wxWidgets: Version 3.0.2 (debug,wchar_t,compiler with C++ ABI 1002,GCC 4.8.4,wx containers,compatible with 2.8)
Platform: Linux 4.4.0-116-generic x86_64, 64 bit, Little endian, wxGTK
Boost version: 1.54.0
Curl version: libcurl/7.35.0 OpenSSL/1.0.1f zlib/1.2.8 libidn/1.28 librtmp/2.3