Perforce: File tampered with after resolve - edit or revert

I'm doing an integration in Perforce and am being met with the following:

p4 integrate -1 -d -i -t -r -b my_branchspec
//Foo/file.txt#6 - integrate from //Bar/file.txt#6
p4 resolve -am
/Foo/file.txt - merging //Bar/file.txt#6
/Foo/file.txt tampered with before resolve - edit or revert.

It seems no matter what I do, I am unable to make this issue go away: the next forward integration will show a similar message.

The file is a text file. I can confirm that the MD5 hash for both files before the integration takes place is the same. What other issues might be going on with this file that I can resolve to fix this nagging message?

Doing a forced resync (sync -f) of that particular file and then resolving theirs (resolve -at) (since I did not touch the file) makes the issue go away.

By any chance are you working in a mixed OS environment, in particular Mac and PC?

We are currently investigating an issue where files are disappearing after resolve (without an error!) on a pc. The file type is "apple" (but shouldn't have been/doesn't need to be. Unfortunately we have a lot of these files already in the depot).

The current workaround is to do the integrations on a mac.