With you there, HV! We've experienced the same in Mexico.... routinely anchored a mile or two inshore according to the plotter...
These are great tools (I do think they are more than 'toys'...) but no substitute for common sense and vigilance.
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)