setError doesn't update/show the error message unless isModified is called

If the value is not modified before setError is called then you must also call isModified afterwards. I didn't find this documented anywhere (it was pointed out on stack overflow http://stackoverflow.com/questions/12491069/can-i-manually-add-error-messages-in-knockout-validation) so it seems like incorrect behaviour to me.

Example can be seen at http://jsfiddle.net/fq1098pu/. Uncomment the isModified line to see that this fixes the issue, but probably shouldn't be necessary.

Reproduce the behavior in the linked JSFiddle by calling setError before isModified, then locate the validation code that handles those calls. The issue is done when the error message is updated and shown without requiring a later isModified call; add a regression check if the repository has tests for this behavior.

Written by the indexing model from the issue text.