I found the following two issues on a fresh installation:
1. Created a custom field of type "String", checked "Required on Report" and linked it to a Project. However, I was still able report an issue without entering any data in this field even though the red asterisk (*) was shown on that field.
2. Created a custom field of type "String", checked "Required on Resolve", and linked it to a project. Again, I was still able to resolve (and fixed) the issue successfully without entering anything in the custom field even though the red asterisk (*) was shown on that field.
I am using Mantis 1.1.8 and I really surprised to see this behaviour. Almost makes me feel like I am doing something incorrectly.
Custom Field Required Bug(s)
Moderators: Developer, Contributor
Re: Custom Field Required Bug(s)
This has been fixed in version 1.2
http://www.mantisbt.org/bugs/view.php?id=10670
http://www.mantisbt.org/bugs/view.php?id=10670