Sorry, I didn't check anything before posted that.
I guess Vifm does not affect this, although I might have edited a Bash configuration script according to a Vifm manual that might have affected it.
There is always only one line.
If, after the last call of the shell from Vifm, I returned to Vifm using "exit", next time I open the editor from Vifm, the only line is "exit".
If I just executed anything and didn't exit to Vifm, that will be the only line.
If I open the editor not from Vifm, but after exiting Vifm, the only line is "vifm".