South's PASS was preceeded by a long pause . . . not 90 seconds long or anything, but longer than normal even given the huge pre-emptive action by E
As West, I called the director immediately after North's 5♦ call. (I was advised by another player after the game that I should call immediately upon the pause.) The director came back after the hand, and I stated that I was not accusing anyone of cheating and that I simply believed that PASS was a plausible call in the balancing seat after 4S. I thought this was/is the standard. (Director told me it's not, FWIW.)
When my partner's do this, I PASS unless bidding on is mandatory with my holding. One example where I did bid on was where I had passed a bad AK, A (honors in short suits) hand in first seat. My partner emerged with 1S in 3rd seat, RHO overcalled 2Hs, I x'd, LHO bid 4Hs, partner paused and passed, RHO passed and I x'd with 3 QTs opposite a partner who opened.
Short of something that clear, I generally feel ethically obligated to pass.
Am I being too strict myself?