PDF has different layers than the imported version
Please see these PDF files: layered pdfs.zip
These files are placed into an InDesign document with some layers turned off using the Object Layer Options.
When replacing one file with another, InDesign tell’s me the PDF has different layers than the imported version, and then makes all layers visible.
However, in Acrobat, I cannot see any difference in layers for these two files.

These PDF’s are generated using another InDesign document. I have the source INDD for these, but not the export settings which have been used to generate the original PDF.
There is surely a difference between the two PDF files (different filesize and probably different color settings), but nothing that seems to be related to the layers. The PDF version also the same (PDF 1.5 / Acrobat 6.x)
Any ideas why InDesign is seeing a difference?
I have a lot of similar linked PDF files. I want to have peace of mind to update the source document and have InDesign retain object visibility of the original links.