For your first problem, I guess you might be pressing the record footswitch again to stop recording? If you do that, it goes into overdub mode, so by the time you turn it off, it's already overdubbed some stuff onto your loop. If that's what's happening, just make sure that when you've recorded your loop, you press the play footswitch instead. That'll stop recording and just play the loop instead without overdubbing.
For your second problem, about switching patches, it's to do with the pre and post modes of the looper. They determine whether the looper is before or after the signal chain. If it's in "pre", you can see in the signal chain view (the view that shows all the effects as little boxes), the box that looks like a tape is on the left side, before all of the effects. This means it's recording the raw input (without any effects), and when it plays back, whatever effects are selected during playback are applied to the output of the looper. It sounds like this is the mode you're in. If you change it to "post", the little tape box is on the right side, after all the effects. It records your playing with the effects already applied, and when it plays back, no more effects are applied to it. It sounds like this is the mode you want. For instance, if you want to record a loop with some preset, then play the loop, and switch preset, so the loop still has the first preset but your live playing has the second preset, "post" mode is what you want.
You can switch using FS3 when you have the looper on the screen. You can even switch after recording a loop, while it's playing: you can record in "post" mode to record some effects, and switch to "pre" so that further effects will be applied to it.
