On some backends, measuring the same expected value twice to the same classical register always leaves that classical register in the "1" state. I don't know if these results will hold over time, but when I ran the following code the outcome was striking.
OPENQASM 2.0; include "qelib1.inc"; qreg q; creg c; measure q -> c; measure q -> c;
This program should always produce "0" in a simulator and generally produce "0" in a real device. Instead, the results are:
As a programmer, I think writes should be independent and the last write should win unless I explicitly allow some kind of quantum fuzziness.