Unanswered Y home no longer working

Hey all,

I'm working on recalibrating and fine tuning an R1, and I've just recently ran into a unique problem. My Y axis (bed) is no longer homing properly, using MatterControl. I was able to use the software's built-in home functionality in the past (meaning, a couple of hours ago at the latest) and have run several successful prints over the past few days.

Pressing the 'Home Y axis' button only causes the bed to move in a positive direction by about a factor of +5; it's actually moving the bed away from the stop switch, not closer to it. Pressing the "Home All" button, or starting a print, causes the X/Z axis to home properly, but the Y axis moves a set distance (roughly half the size of the bed) then stops. This occurs no matter what the initial position of the bed is, and does not move to the same point, but rather the same distance (relative to what its starting position is.

I have checked to ensure that the switch's wires are connected properly, that the belt/pulley system is working properly (no grinding when moving the bed by hand or when using MatterControl's manual control buttons).

The software will not allow the bed to move beyond the stop switch when moved using the +/- manual control buttons, so I don't think it's a physical switch problem; it's only when the printer tries to home does this problem occur (the Y axis simply does not home any more). Any thoughts on what could be causing this, or any additional information that is needed? Thanks in advance!