This suggests the device is running from external program memory. However, the EA pin is strapped to VCC so the device should run from internal Flash. ..... The problem is infrequent; it happens perhaps one time in ten power-ons.


From the datasheet: "the status of !EA is sampled at reset..."

If you are not using a proper supervisor chip, I can see a problem with the sampling of !EA which might occur with somne chips at one end of (but within) the tolerances.

Are you using a supervisor chip?

Erik