When zooming in or out text will at times disappear and then reappear.
Go to Workspace>Preferences>View OptionsTurn anti-aliasing option off for text.This option is used to make text edges of certain True Type fonts look smoother. This setting actually affects hardware anti-alias settings when doing a regeneration of graphics.
http://communities.bentley.com/products/microstation/w/microstation__wiki/14794.text-displayed-on-top-of-other-elements-when-priorities-are-equal.aspx
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