Thanks, Shonky!

Let me clarify the question a bit, to give you some more context.

The Betz board is indeed using a 2.5v linear voltage regulator at position U4, and in the past I have measured it at 2.5v when the board is all by itself and getting its power from its USB connector. Peter has deliberately designed his board to run the chip at 2.5v in order to make it use less battery for situations where it's battery-powered. The schematic isn't wrong, and there's no damage or failure, the board works fine as is.

What I'm saying is that I, in my PCB design which attaches to this Betz board, am doing things differently, on purpose. Here's what I'm doing:
- Deliberately choosing to run the whole thing "always-on".
- Deliberately choosing to run it at 3.3v instead of 2.5v.
- Deliberately choosing not to use a battery at all and instead running the thing at constant DC supplied 3.3 volts.

To get this to work, I must personally apply 3.3 volts to the following three pins at the edge of the Betz board:
- BATT
- ENA
- 3v3
- I'm also cutting JP4, the "5v power" enabler for the FTDI Uart chip.
- I'm also very carefully NOT applying 5v to the Vin pin on the edge of the board, and not connecting a USB cable to it.

Those things are what's required for me to make this thing work as an "always on" device at 3.3v.

When I apply 3.3 volts to those three pins I listed above, that means that, as far as I can tell from the schematic, I'm applying 3.3v to both sides of that 2.5v linear regulator at position U4. Simultaneously I'm making the little on/off switch totally useless since the 3.3 volts is now going to both sides of the switch anyway no matter what.

As far as I can tell, everything works this way. At least, everything works the way I want it to work. There's no failures occurring here as far as I can tell, everything seems healthy.

So my questions essentially are "why is it fine with this"?

More specifically:
- If I am deliberately applying 3.3 volts to those three pins as I described above, are my assumptions about where the 3.3 volts goes true?
- If true, why does it work? Why don't I have problems because I'm putting 3.3 volts to both sides of that linear regulator at U4? Mark has previously talked about problems occurring when I try to put two "output" voltages into the same place. Why isn't that causing a problem here?

Really this boils down to a single generic question:
- If I have a linear regulator of that type, with a 5v input and a 2.5v output, what is the expected behavior when instead I apply 3.3v to both its input and output lines, and why?

If I think of a linear regulator as just a way to reduce voltage like the voltage dividers we've previously discussed, then it makes sense that the regulator would just "do nothing" in that case, there's the same current on either side of it so there's nothing for it to do. Is that really what's happening here? Or am I misunderstanding how one of those linear regulators works?