I am using 2.18.10 64 bit with exactly this problem, but now have a reason and solution.
I copied all the symbols displaying half only to another directory, and they were fine. Then I deleted all the original symbols in that directory, and the halves are back. Obviously, one of the symbols already in the directory was controlling the appearance, so as soon as that was deleted, the problem came back.
Second, when I added another symbol to the end of the directory displaying half symbols, they were all then fine (I added the tram stop). If I removed this, they all became half again. The last symbol in a directory appears to control the appearance of all of them.
You can probably just change the last symbol in a directory to get rid of the problem, but I changed all mine. Using Inkscape, look under document properties. Simply make sure that the document size has equal height and width, i.e. a square box. If the last symbol is a rectangle, with height less than width, all the symbols will be cut.
Of course, this does not affect the plotted symbol. It just makes selecting a symbol a bit harder... and annoying.