Colleagues,
An update on this topic, since I did as suggested (connecting 10K pull up + 4k7) and noticed same behavior as mikcaau mentioned. Investigating the logic levels, it turn out that the 4k7 R is too high (combined with 10K). With the suggested set up, V rain = 1V (aprox),and anything above 0.8V is considered ambiguous (not guaranteed, for a 3.3v power supply) .
I like the idea of a protection and thus a serial R , but the value should be lower . Like 1K or similar (with 10K pull up) .
Cheers,
martin