There are two different ways one can make a weaver's knot. One has both ends on the same side (a) the other on opposite sides (b).
Pictures and a statement "the two free ends should end up on the same side of the knot" can be found on wikipedia and many other websites.
I could not find any source for this statement, but an experiment with 10 mm rope shows that (a) deforms when pulling while (b) conserves the form. My experience was also that (a) was not so secure, which seems to be caused by the fact that the pulling direction is also the opening direction of the knot. In variant b the directions of force are antiparallel and the knot fixes it self under tension.
Where can I find a trustworthy source about the safety of the weaver's knot variants?