SVG: adding shadow filter makes straight line invisible

Question

I'm trying to add a shadow to my SVG. It works well with all 2D objects, but when same filter is applied to a straight line (either <line> or <path>), the line becomes invisible, and no shadow is added.

Demo: https://jsfiddle.net/ccj0Ldfh/1/

Answer 1

Per the last paragraph here

Keyword objectBoundingBox should not be used when the geometry of the applicable element has no width or no height, such as the case of a horizontal or vertical line, even when the line has actual thickness when viewed due to having a non-zero stroke width since stroke width is ignored for bounding box calculations. When the geometry of the applicable element has no width or height and objectBoundingBox is specified, then the given effect (e.g., a gradient or a filter) will be ignored.