Horizontal Curve Set - Stationing Not accepting the Datum reference.

Hi

I'm using Power Rail Track Microstation. In horizontal Curve set - Stationing I have provided a chainage 171797.472m to the Down Main string.

But the string doesn't allow me to change to Ch.171797.472. Instead its to the original chainage Ch.171790.124.

Any help would be appreciated.

Shoaib