Firmware version on the eTrex?
GPS tells the unit GPS time[1]. It doesn't tell it how to convert that to UTC or any other timezone - it needs a database to look that up, which will be part of the unit's firmware. I could imagine mysterious undefined behaviour if the database didn't contain a fudge factor for the current GPS time.
GPS time's epoch was 1980-01-06-00:00 UTC, so throw in a bit of millennium bug, and I can see how you'd get 1935.
Try upgrading the unit's firmware.
[1] A straight count of weeks and seconds since the epoch - no leap seconds, so it gets further out of sync with UTC as time goes on.