Can't create/switch to form if other form with similar name exists

[Herbstkind]

Steps to reproduce

1. Create a form: tp!form Felia add test https://avatars.githubusercontent.com/u/87663327
2. Create another form whose name is a substring of the name of the first form: tp!form Felia add es https://avatars.githubusercontent.com/u/87663327

Expected behavior

Second form is created

Observed behavior

Creating the second form fails with Felia already has a form matching 'es'

notes

Same behavior when I rename another form to es.
This seems to be a matching problem. My guess is that you're using a regex without ^ and $.