yes have seen this in a couple of cases; where they reduced or discontinued iodine, but still took the selenium.
"It seems logical that for some nutrients it is best to ingest small amounts over a long period of time"
-yes, like selenium and others that accumulate in the body, with a loong half time in the body.
Thats why I started high (800mcg of selenium!) then reduced to like now; 200 mcg every other day. then you have the soil; over here it is very low in selenium, but other areas like in the US, is high. Yes, the minefield.
Needs to be taken into consideration, when supplementing.