I was able to fix this in the .js code, by commenting out the following line as follows:
/* j.style.height=this.def_line_img_y; *
in the file: /sources/dhtmlxTree/codebase/dhtmlxtree.js
in the function: dhtmlXTreeObject.prototype._createItem()
The explicit height causes the image to stretch unless you set the height perfectly in your own code. With the liine commented out, the height of the tree lines finds it’s own level and doesn’t attempt to stretch the line/image vertically.
I would propose Darya, Alex, et al consider making this change to the codebase so we don’t have to wrestle with this issue anymore. I know i spent a -lot- of time finding the root of this…