[Y_Y]

It's not a mistake

[mirekrusin]

If it's not a mistake then why they took it off?

[cmacleod4]

The original design decision was to behave like a shell, where ~ means your own home dir and ~fred means fred's home dir. With the benefit of experience, this is now seen to be unwise and a different decision has been made.

[eviks]

So they copied the mistake from some shell (you don't need much experience to realize it's unwise not to use a separator to separate)