Comment 3 for bug 1432661

In a new document, the initial pattern source (until edited by the user e.g. by pasting a path on the clipboard as pattern source) is a short straight line of the length of 1 SVG user unit, starting at the SVG origin (usually the top-left corner of the document's page area), with path data "M 0,0 1,0".

AFAICT the initial pattern source when applying the 'Pattern along Path' path effect via Path Effects editor has not changed (it is basically the same with 0.47, 0.48.5, 0.91, 0.91+devel r14495 - except that 0.91+devel now produces a slightly different notation of the path data ("M 0,0 H 1").

Not changing the report status to 'Triaged' myself - I was not able to reproduce the "bug" as reported in any of the tested Inkscape versions in a new document (neither was the pattern source missing ("no control path segment"), nor did I have to hide the path effect to get access to the two nodes of the initial, unedited placeholder pattern source).

Likely related earlier reports already tracking the underlying issue:
Bug #682851: Shape in "pattern along the path" should be in top left of the shape
Bug #518703: Pattern Source for "Pattern Along Path" should automatically be visible, regardless of canvas zoom depth