Single pole switch acting as a 3 way switch?

I'm mistaken about the traveling wire what I meant was the wire coming off the single screw on one side.


I'm having a problem with my 3 way switches. Downstairs there are two 3 way switches which control the 1st and 2nd floor hall lights there is also a 3rd switch which appears to be a simple single pole switch all are in the same box and share the same traveler wire. The two 3 way switches are acting like typical broken switches (they only work when one switch is on). I replaced the switches and they still acted the same even when both sides were replaced. Now here is the part that I don't understand. The single pole switch has the traveler wire attached to one terminal and controls another ceiling light right inside the front door. However the second switch (also a single pole)does not work at all even when a new switch is installed. Also this second switch only measures 45 volts. There is a third single pole switch in the same box pole(also attached to switch that doesn't work, the one with 45 volts) that is suppose to control an outside light but has only 105 volts. I disconnected these two single pole switches thinking that they were possibly the problem however it had no effect on the three way switches they still don't work as they should. The house is 80 years old and everything looks to be original except the two single pole switches with the low voltage.

 

Did this ever work correctly? If not this is one of those situations where I would disconnect everything and go from scratch. We may not need to do that but there are some things we need to correctly identify.. Lets start with: What are you calling a traveler wire?