I'm using spectacle with the i3 window manager, and in some circumstances the region captured is incorrect. It's possible that this problem stems from i3 not setting properly the window properties. However I don't remember having this issue with KSnapshot, and other snapshot tools with similar functionalities produce the expected result.

Reproducible: Always

Steps to Reproduce:
1. Use i3wm
2. Set a window floating (away from the top left corner of the screen), or in an vertical split, not on the left hand side of the screen.
3. Start spectacle and select windows under cursor
4. Take a screenshot of the floating window or a window on the right hand side of a vertical split.

Actual Results:  
Spectacles captures a region that appears to be of the right size, but instead of it being the window clicked on, it is a region starting on the top left corner of the screen.

Expected Results:  
Actually take a screenshot of the window that was clicked on.

A few examples demonstrating the issue:

First setup, trying to capture a dialog window:
- Desktop: https://i.imgur.com/oRYaX5o.png
- Screenshot obtained by clicking on the dialog window: https://i.imgur.com/1d1abEu.png

Second setup, trying to capture a window on a right hand side of a vertical split:
- Desktop: https://i.imgur.com/vtr02W6.png
- Screenshot obtained by clicking on the terminal on the right: https://i.imgur.com/UtKrnb0.png

Third setup, slightly more complicated splits:
- Desktop: https://i.imgur.com/7TkhPdB.png
- Screenshot obtained by clicking on the terminal on the bottom right: https://i.imgur.com/kCK8fjO.png

In this third case, clicking on the two other windows produces the expected result.