Changing work item types affects source control

You'd ask how will changing work item type affect source control? My first answer would be - it will not really change anything as only connection between source control and work item tracking is through changesets or files association to work items. But it turned out not to be not that simple.

Let's say that you have introduced new validation rule as a result of work item type change, and some field that was optional become mandatory. If there were existing items at the time of the change, that will mean that upon changing and saving any of these items you will have to specify value for the field that become mandatory. But how that is related to source control?

Here goes the scenario: you are checking in some files and want to associate them with work items in "Pending Changes" window, and work items have data that become invalid as result of work item type conversion. The files to check in are selected, work items to accociate with are selected, you hit Check In - but that's no go! The following message is displayed (clicking on image will display larger screenshot):



And if you think about it some more, it really makes sense since the default check-in action for changeset and workitem association is "Resolve", and that will require
work item modification.

But what about changing that check-in action? Let's change that to "Asscociate" and see if check in will fare any better. No luck here (and I would say the result is even worse) - files are checked in, changeset is created but association to work items is not created, as seen on the following screenshot (clicking on image will display larger screenshot):



In that case, I am not so sure that the behavior exhibited is one expected. I am doing the association between work item and some other artifact, should the full validation be performed? And why the validation is performed after check in?

To conclude, that would be wise to handle data conflicts in existing work items as part of work item type modification. When you have hundreds of work items and modify the type, you do not want all your developers fill in the missing data - that is clearly part of conversion (and I am not talking about breaking changes; making several fields mandatory can seriously affect productivity).