Digital Light & Color

Scenario :
After opening an image, the readout tool is turned on and used.
Then the File Open command is modified to switch the current file. Click OK.

Another image is displayed.
The readout tool is stuck, ceasing to respond to mouse clicks.
If the image has different dimensions, the readout tool can show negative coordinate values.

To re-activate the Readout tool, you just need to click on its dialog box.

I recently modified the Readout tool so that when it is open, it automatically repositions the cursor to the last readout position every time the current image is changed. This was motivated by wanting to allow using Ctrl-D to flip back and forth between an input and output image while watching the Readout tool update. If you don't reposition the cursor for this scenario, you can't tell what point in the image the readout tool is positioned to.

Unfortunately, this leads to a lot of other confusing behavior such as you have reported, so I will remove the cursor repositioning for now until I can think of a better way to implement it.