In an Image Service, only one legend entry shows on a Legend Image in an HTML Viewer if the EXACT 'value' attributes for two VALUEMAPRENDERERs are the same, but the VALUEMAPRENDERER 'lookupfield' is different.
<EXACT value="30" label="1990 Population">
<EXACT value="30" label="State FIPS">
This is a problem when there are two VALUEMAPRENDERERs inside a GROUPRENDERER. In this scenario, the VALUMAPRENDERERs have a different lookup table but the value for EXACT is the same. The ArcIMS Spatial Server keeps track of only the first EXACT value even though there are two VALUEMAPRENDERERs. This leads to one, instead of two entries in the legend.