There is an issue with WordPress multisites where if you are in a child site, the lost password link will point to the parent.
So say your site is /parent/child, the url would be:
This also affects the reset password link in the email that is sent.
There are a couple of fixes for this here:
I've applied tried both and they fix the problem.
However, when I activate Sideways8 Custom Login and Registration, the problem comes back.
I've had a look at the files in the plugin /inc folder, but can't see anything.
Can anyone help?