KWMT has been known to do this. A couple years ago, they went several weeks with daytime power at night. They almost sounded like they were a “local” here in Central KY. BTW, KWMT has a tremendous Daytime footprint. I drive across Missouri and Kansas each summer and can carry them on my factory installed Bose system in my 2006 Silverado from Central MO almost to the Colorado border on I-70 when a Spanish language station from NM takes over on 540....
WAUK from the Milwaukee area rules 540 around here, but if you null their daytime signal, you can usually hear KWMT perfectly audible underneath. (At night, WAUK typically mixes with a somewhat weaker CBK).
As for KWMT staying on day power overnight.... They're not a particularly serious repeat offender, but it happens from time to time.