Text scales when attached as a reference.When a model containing text is attached as a reference, the text in the reference is too big and is scaled compared to how it displays when opened on its own.
The text when placed in the original file has been placed with the Annotation Scale Lock switch on. This means any text placed with this lock on will respond to a change in annotation scale in the active master file model.To set the reference text back to desired (normal) scale, this setting must be turned off.
Scales in MicroStation - Blog
Annotation Scale and the Drawing Scale Dialog - Blog
Annotation Scale simplified - Wiki