I found a problem that also seems to be an issue on the Pie Register site itself.
1) On my own Pie Register enabled site, I created a user name that has a whitespace between first and last name.
2) I went to reset the password via an email notification.
3) In the email, the URL had not encoded the whitespace (did not put %20 in the white space) and the URL cuts off after the first word in the user name. The second name is visible in the email but is not part of the link)
4) This caused a bug. The full user name is not part of the link and the link is broken. The only way to fix it is to cut and paste the full url and the final word of the user name from the email, paste it into the browser’s address field, and manually type in the %20 between the two words of the user name.
5) I decided to go into the code and find where the user name is being appended to the reset password URL but got lost in a sea of PHP variables.
6) Another option is to restrict the whitespace in the registration form. but I don’t see any such restriction in the form builder.
7) An ironic twist: When I went to this site to type this problem, I couldn’t remember my password, so I clicked on Forgot Password and got an email where the last word in my user name is cut off from the URL because I put a whitespace in my user name (i.e. “Richard Behrens”).
So this site has the same issue for anyone who creates a user name with whitepsace in it.