Crop not working (for me at least)

[Noteworthy]

I'm at my wit's end!

Okay, so I have this image that I have rotated to my satisfaction.
Using the crop tool I have selected to area to retain and thereafter I click on the selected area to effect the crop.
The excluded pixels disappear but the canvas does not get cropped.

I'm sure I've done something wrong somewhere as this has never happened before.

In the crop dialog box nothing is checked except for the highlight at 50%.

Mode is Normal.
Many thanks