This was happening to me and I came here to find an answer. I didn't scroll far before I saw someone else with the same problem. Are you using chrome? I am (and so are they) and they mentioned that downloading the LastPass browser extension fixed it for them. So I downloaded it and it fixed it for me. I didn't even finish setting it up before I went back and checked. Sure enough, my passwords were showing correctly and not changing in those 2 seconds! Computer only though. This person said it was still happening in their app (which I don't use, so cannot confirm or deny). There may even be another solution but I didn't feel the need to keep researching. Good luck!
Thanks for sharing this. I'm using Chrome and already have the extension but still have the problem with opening site fields and Lastpass quickly filling in the wrong password. Very frustrating. I'll keep searching for other remedies. Glad the extension worked for you!
