Steps to reproduce:
1] Start WinSCP from W:\applications\winscp and login.
2] Change local path to W:\.
3] Change drive to W:.
Result: local path is now W:\applications\winscp.
Expected result: should stay in W:\.
Apparently, this happens when the last path on the drive was it's root directory. When the program has been started from the drive where the binary resides, it's jumping to the directory it was started in. When started from another drive, then changing drive to the "starting" drive makes a jump to the starting dir and changing drive to the binary drive, it jumps to the binary directory.
I hope it'll make sense to you.
I use WinSCP v18.104.22.1681, Windows 7 Pro.