I've never seen a Diseqc Switch with an input for OTA? Which makes me think the switch is a Multi-Switch. The picture you posted above is not good enough to read the labelling on the top of the switch, due to the angle the picture was taken from. If you could tell us what all is said on the label of the switch it should be helpful. If it is a Multi-Switch, the 2 sat inputs are probably one for V and one for H. I've seen European websites that label some switches as "Diseqc Multi-Switch"s. I don't think these are what we on this side of the pond consider Diseqc Switches, but we would refer to them as Multi-Switches.
At any rate, my ranting is trying to say, if it's a Multi-Switch, you are getting Vertical from one satellite and Horizontal from the other satellite. And, it's quite posible that the one you appear to get nothing on, has no TP's on that particular polarity. Also, if it is a Multi-Switch, you probably don't have the settings in the receiver correct?
I'm just totally throwing crap out there in an attempt to spark a thought that may or may not rattle the answer out, from wherever it is hiding?
Hope you find the culprit sooner than later It's probably something really simple? Good Luck!
Al