Comment 1 for bug 1656177

Not limited nor related to the (experimental) LPE Tool for geometric construction: this is node snapping to rectangle shapes in general, and reproduces with these steps:

1) launch Inkscape 0.92 with default prefs
2) draw a rect
3) round its corners
4) switch to the pencil or pen tool
5) hover the corner of the rectangle and inspect available snap targets

--> the only available snap target for cusp nodes (default snapping mode in drawing mode) is the regular corner of the shape independent of any rounding applied via rectangle tool.

6) activate snapping to smooth nodes on the snap controls bar
7) attempt to snap to the start/end of the arc of the rounded corner (assuming a smooth node on either side)

--> no snap target available

8) convert the rectangle to path (Shift+Ctrl+C)
9) repeat snap tests

--> node snapping finds targets on the converted path as expected.

This snap behavior has been observed in Inkscape 0.47, 0.48.5, 0.91 as well as in latest 0.92 (i.e. always): the start/end points of a rounded corner of a rectangle shape are not targets for smooth node snapping.

Neither the original bug description nor the screenshots reveal whether snapping to smooth nodes was enabled by the user - the report might actually be more a question about usage (outside the scope of a bug tracker).