The cards are being swapped out.

[stormcat664]

I'm not a native English speaker and am using translation tools, but I hope this gets the point across.
I believe this started happening in recent versions: when switching to list view to reduce duplicates in a decklist, if multiple versions of a card exist within the deck, the version with fewer copies automatically sorts to the top. This leads to unintended mistakes.
This behavior is extremely annoying when trying to swap basic lands into a different version, for example.