We've marked the target version field in our defect and feature trackers as a required field if the issue is at least in the "in progress" state. This was done to ensure, that no issue will fall under the table during version planning. Additionally to our customer projects, we have one project which is used as our internal IT helpdesk. This project has no target versions defined. Therefore, the validation of issues failed with the error message, that a target version is required.

I think that this is an erroneous validation failure, because if the project manager does not specify any versions, requiring a not specified version is not helpful.

How does other teams solve this issue?

I can confirm this behaviour for 2.3.0.stable (don't now the exact SVN revision) as well as for 2.3.1.stable.11984.