I get the same result using this example. It's not documented explicitly, but it makes sense. Empirically, only the combined (shared) axis supports panning, even if the subplots would otherwise support panning on the orthogonal (independent) axis:
CombinedDomainXYPlot
supports domain panning; invokessetFixedRangeAxisSpaceForSubplots()
indraw()
.CombinedRangeXYPlot
supports range panning; invokessetFixedDomainAxisSpaceForSubplots()
indraw()
.