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.
".. 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)
1984 Fast/Nicholson 345 "FastForward"