#3 First crop always uses default canvas size

[Mathijs]

The first 'crop' operation does not crop to the selected area, but to an area of the default canvas size. If the image is smaller than the default canvas size, the remainder of the image is filled with white.

Steps to reproduce:
1. open an existing image with Paintbrush. For example, the Paintbrush icon at http://paintbrush.sourceforge.net/rw_common/images/newicon64.png
2. click the 'retangular select' tool
3. select a part of the image
4. click Image -> Crop

Expected behavior: the image is cropped to the selected area
Actual behavior: the image is cropped to the default canvas size. The upper-left corner of the cropped area is the same as that of the selected area.

This only happens the first time 'crop' is used. The second time and onwards crop works as expected.

Environment: Paintbrush 2.0.1, Mac OS X 10.6.4.