Horizontal slider in "Power Stroke" LPE not movable with mouse correctly

[Ron Burk]

The "Power Stroke" LPE uses a horizontal slider control with the "Smoothness" parameter. I'm not sure why it's there, since there's already an up/down scroll. If this control is used elsewhere in Inkscape, I haven't found it yet; I've confirmed it's not used in any other LPE.

The problem: when you click-drag the horizontal slider, it moves only a short distance and then stops, making the control fairly unusable.

a) Select Pencil tool.
b) Set "Shape" in toolbar to "Triangle in"
c) Ctrl-Shift-7 to open Path Effects dialog
d) try to move Smoothness horizontal slider back and forth.

Windows 7 Pro, 64-bit
Inkscape 0.92.0 r15299

Animated GIF demo: https://drive.google.com/open?id=0B-DCrkRG5wblMEdKdlNtckFDdGM

Another user confirms same problem on Linux Mint 18:
http://www.inkscapeforum.com/viewtopic.php?f=5&t=31678

[su_v (suv-lp)]

Attaching externally linked GIF file to bug report (links tend to expire or otherwise get lost; the reporter's attachment is a html page with lots of javascript, not the GIF itself).

[jazzynico (jazzynico)]

Reproduced on Xubuntu 16.04, Inkscape 0.91 and lp:inkscape/0.92.x rev. 15345.

As a workaround the entry box and its spin buttons work as expected.
But... do we really need a slider here?

[su_v (suv-lp)]

Also reproduced with oldest trunk build archived on this computer (with OS X 10.7.5) which has (at the time) experimental path effects enabled:
 lp:inkscape r10795

[Jabiertxof (jabiertxof)]

Fixed in master in r.e96c6827, not backport to 0.92.x in mind.