Blueprint with `Relative` option in `Snap to grid`

[datarza]

Blueprint with `Relative` option in `Snap to grid` freezes sometimes. It looks like `Shift` key was already pressed before blueprint was selected (dragging started). The bug is not easy to reproduces, but it happens a lot of times.

Possible (no warranty) way to reproduce it:

1 select blueprint with relative option
2 Press Shift key
3 Place blueprint and dragging it several times
3a Alternative, drag just a little, without placing the blueprint second time
4 Clear cursor (Q key)
3 Select another blueprint with relative option
4. The behavior for selected blueprint will be like `Shift` key was already pressed (dragging started)

Probably, pressing the Q key does not reset the dragging for blueprint.