ArcMap allows the use of BMP and EMF graphic file formats as fill for picture marker symbols. However, after zooming in to a small map area to a scale of, for example, 1:326 or more, the picture marker fill may disappear.
This is a known issue.
ArcGIS Desktop 10 workaround
▪ Add the layer to a basemap layer as the symbology will not disappear when zooming in.
ArcGIS Desktop previous versions workarounds
▪ Use a character marker fill, instead of a picture marker fill.
▪ Convert the symbology to a representation.
See the link for the ArcGIS Desktop help topic 'Managing feature class representations' in the Related Information section below for more information.
▪ Set the map scale to a smaller scale to display a larger area of the map.