Mine will stick sometimes for weeks or maybe even months. I think it switches when they push out an update, it's totally unpredictable when it will happen. At least on iOS, it usually notifies me that it's switched so I know I need to switch it back.
Is there a TweetDelete like service that resets this setting regularly?
I realize it shouldn’t be necessary. I’ve mostly stopped using Twitter, but I ask out of curiosity.
I'm not aware of one. As @eyelidlessness pointed out in the comment above, it seems to change back randomly, so I think it would be hard to detect when it changes.