Another EE question, Mark.

On my current PCB version, which appears to be working just fine with three different Betz boards, I'm applying 3.3v to the BATT, ENA, and 3v3 connections on the Betz board.

According to Peter's schematic, that looks to me like I've got 3.3v sitting on both the VIN and VOUT sides of that little 2.5v voltage regulator ("U4") on his board, regardless of which position I set the "smd_2_pole_switch" to.

Why does this work without any apparent ill effects?