bizarre guide drag-create scroll glitch

Migrated from: https://bugs.launchpad.net/inkscape/+bug/168553

If you disable the rulers, you can still create guides by dragging the edge (if you try hard enough).

On Linux it appears to work with the left and top screen edges. On Win32 only the left one works.

And now to the really weird stuff. On Win32 if you try the top edge several times the canvas occasionally scrolls down by 1-2 pixels (same with the left edge, but it scrolls to the right).

The same behavior was observed on Linux.

The glitch exists since 0.45 (till 070411).

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Eventually one shouldn't be able to create guides like that if the rulers are disabled. It's almost impossible to create guides intentionally this way. And if it does happen you wonder where they came from.