In QGIS 2.18.14 Processing Toolbox I started to use
v.buffer.distance to create fixed-distance buffers around my lines.
I can also make the buffer with square caps (straight ends).
However, I cannot make it without end cap. I mean, the option "Do not make caps at the ends of polylines" does not seem to work.
This is similar to this recent question v.buffer.distance does not create straight buffers in QGIS, but my situation is different, as I can make square caps (-s) while not being able to cut caps (-c). (Probably @Annekeds is using QGIS - GRASS plugin, while I am working through Processing Toolbox).
Strangely I can make buffer without caps when I run
v.buffer.column... so my workaround for now is to use
v.buffer.column with same distance in the field.