I just rated a card with easy before it was due and it reduced the interval which makes no sense
At the very least should keep the old interval. A card is not going to get worse by successfully remembering it
I also rated a card due around a week ago easy and it got an interval of 1day. Which made think algorithm doesnt take this into account at all
If the card is successfully answered, its stability does not decrease. If there have been no changes in the FSRS parameters.
I havent manually touched FSRS parameters if thats what you mean
Have you re-optimized your parameters since the last time the card was reviewed? Or changed what preset the card is in, or the Desired Retention for the preset/deck?
Very unlikely but i dont know tbh
i see how that could rightfully reduce an interval for a card
Ill check those things next time 
also, just to make things clear, which of the following scenarios what the one that happened?
did you have a card that was due in X days, you rated it today and its new due date became <X days in the future?
did the card have an interval of N days last time you rated it and now it got an interval of <N days?
did you rate a card Z days after the last review and got a due date that is <Z days in the future?
the last one is definitely possible, even without toying with parameters. same for the second scenario that you posed, which fits my third option exactly. i don’t even think it’s necessarily that rare. the goal of the algorithm isn’t for each review to be harder than the last one, but for the next review to have a DR% odds of you remembering it. if a card is overdue and the algorithm thinks you have just a 50% odds of remembering it, that doesn’t mean it necessarily has to wait just as long until the next review, rather it should wait as long as needed for the odds to be DR%, which may indeed be less than the time since the last review, especially if you haven’t optimized in a while. and also, if you optimize again while enabling rescheduling, that card might very well be pushed into the future (though i’m not nearly enough of an FSRS expert to say for sure).
Not sure i follow all your cases but what i did was to i rate a card that was very close to due in the browser where i can see the interval and it was something like 15 days. After i rated it easy, the interval went to 7 days
Now i have noticed myself that intervals dont get updated until you rate a card. So is very easy for a card to have a wrong interval
Its just a shocking thing to see (an interval going down after rating a card easy), but now i understand that intervals is not the real interval of the card, its the interval that was set the last time the card got rated
Am i getting this wrong?
That’s correct – what was set the last time the card was rated or scheduled/rescheduled. Though I’m not sure what you would consider to be “the real interval” if not that.
Well, if the interval was the real card interval i would never see it moving from 15 to 7 after rating the card easy. 15 was not the up to date interval for that card
The interval is set when the card is graded/scheduled/rescheduled. If you change something that impacts when the card should be/have been scheduled, but don’t actually change the scheduling, the interval doesn’t change.
How do i change the scheduling of a card after changing decks with different settings?
I mistakenly thought this was done automatically
It’s not done automatically.
You can use the FSRS Helper add-on to do this if you want the cards to immediately be set to that new scheduling. Select the cards you moved in Browse and run Cards > FSRS: Update memory state and reschedule. That will update the DSR components of the memory state, compute a new interval, and set a new due date for the cards.
I see
Is there any benefit to do this? I mean, is there any problem to not have the interval updated other than visually not having the real interval of the card?
For me, If eventually cards get fixed, i dont really mind having it wrong for a while. I dont move that many cards from a deck to have yet another addon just for this
There’s no need to run a “reschedule” on your cards if you don’t want to. The interval isn’t used for anything else, and it will be adjusted every time you study the card anyway.
thanks