I'm not a fan of the SPST push switches for tape source/record on the P20. I notice a lot of bleed when there's a signal playing thru the tape input but listening to Phono etc. My guess is the toggles on the P10 may be better in this regard. The P20 has MC input though.
Your comment got me wondering about my P30, which has similar in-out switches. I found that, when a source is playing through Tape-1 or Tape-2 there is some audible bleed-through in the other tape input and in the AUX input; it becomes audible in all three inputs only as the dial approaches the 1 o'clock position, fortunately—louder than I could ever bear to listen. Nothing bleeds through into TUNER or PHONO, however; in the latter at least nothing that I can hear through the expected low background noise level in the MM setting (in MC silence is virtually complete, as you'd expect).
When a source is playing through AUX, bleed-through in TAPE-1 and TAPE-2 is there but just barely: nothing till the volume passes 4 o'clock. None at all, happily, bleeds through into TUNER or either PHONO. When a source is playing through TUNER, bleed-through is nonexistent everywhere.
My conclusion, for what it is worth, is that the switches have less to do with the problem—to the extent that it
is a problem—than do other circuitry matters that I lack the competence to discuss or even raise. All I know is that I have heard very few pre-amps, integrated amps, or receivers that don't exhibit similar problems or—rather more frequently—worse ones. Indeed, my old AR X-10 receiver is the only one of its breed that I've ever heard where there is no bleed-through from the (alas, always on) tuner section into the line inputs. (I've heard tuner bleed-through from Luxmans thrice or quadruple its price!)
Ideally, I suppose, one should own enough pre-amps to be able to limit each to a single input source. Ah, to have such cash …