If you could confirm whether this happens when starting Vim in the following ways, that should help narrow down whether this is a bug in Vim or some script that is loaded.
1) vim -u NONE -N testfile
2) vim -u NORC -N testfile
3) vim --noplugin -N testfile
4) vim -u /etc/vim/vimrc -N testfile
Also, attaching the problematic file (or another one that exhibits the same behavior if the original has sensitive information) would help attempts to reproduce the problem.
If you could confirm whether this happens when starting Vim in the following ways, that should help narrow down whether this is a bug in Vim or some script that is loaded.
1) vim -u NONE -N testfile
2) vim -u NORC -N testfile
3) vim --noplugin -N testfile
4) vim -u /etc/vim/vimrc -N testfile
Also, attaching the problematic file (or another one that exhibits the same behavior if the original has sensitive information) would help attempts to reproduce the problem.