PDF, DWG and DXF files linked to SW'x drawing file but not acting like it on check out

I have a user who's contains tab does not show the pdf, dwg and dxf files as linked references but when I check on my computer they do show up.  When I check out the drawing file the pdf, dwg and dxf pull up for check out, his does not.  Any idea why this is happening?

Thank you,

Ryan

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