Dear jmcilhinney,
thanks for your suggestion, but actually I want exactly that behavior. Previously I inserted the RemoveHandler in the if statement in the textboxes_MouseMove routine, but the behavior was not the one that I wanted. I made different tries and the code I posed is giving me the desired effect.
What I'd be interested in knowing is where I should place the Dispose statement as you originally suggested and what is the scope for it.

Thanks for your insights,
A.