In some occasions, the whole matlab session becomes very unstable. This may happen when too many errors have appeared, or if you have worked a long time and used a lot of memory that matlab has not been able to free up, etc... If strange things start to happen like you cannot even synthesize a simple signal with Fraclab or launch a simple command in matlab, it is advised that you simply quit the matlab session and start afresh.
When you perform an invalid operation in a given window, the cursor turns into a watch when you point inside this window, and remains so even if you subsequently launch valid computations, until you close the window in which this happened.
For some reasons, Matlab sometimes flips or rotates the image around before displaying it. Thus it may happen, when you try to view the output of e.g. a denoising of an original image, that the result seems weird. You just have to remember that the data may have been rotated.