I'm using QGIS 2.14.3 Essen on Linux Mint 17.2 Rafaela. I'm digitizing either into .OGR vector file or a Spatialite database. Same happens with both.
I can be digitizing a string, I complete it with right mouse button, I then add in the attributes (automatically created unique id) and save. I then save the element. So, typically I'll then select another string nearby - with 'Select Feature by Area or Single Click' and then I crash straight out. If I haven't saved the line string I've lost it of course.
The message I get from the terminal is:
"ERROR 4: Permission denied qgis.bin: geos_ts_c.cpp:3657: int GEOSCoordSeq_setOrdinate_r(GEOSContextHandle_t, geos::geom::CoordinateSequence*, unsigned int, unsigned int, double): Assertion `0 != cs' failed."