Directories created by XP and Win-7 clients aren't visible to each other

We have a user who has found an interesting misbehavior on our file-serving cluster. He was able to create a directory on his home directory using WinXP and not have it be visible by a Win7 machine. This goes both ways, he was able to create one with Win7 that XP can't see.

WinXP:

Win7:

The server is Server 2008 SP2 in a Failover Cluster. The server only sees the 'testing-7' directory in Explorer and command-line. I checked our backup software, which uses shadow-copy, and it only sees the 'testing-7' directory as well. However, 'Previous Versions' on an XP station happily shows previous versions of the 'testing-xp' directory that are quite visible and obviously usable.

I ran chkdsk against the volume in the off chance that there was some corruption lurking, but it didn't find anything.

Additionally, he was able to create a file called "Arrow.docx" in the same directory on both computers. In this document he saved different data. After rebooting everything, the win-7 machine saw the arrow.docx file with the win-7 data in it, and the WinXP machine saw the arrow.docx file with the WinXP data in it.

The machines used were fairly standard images in our Computer Labs (being in the middle of the XP to Win7 transition, we have both flavors at the moment). I can see all of the files he created on my own stations and they behave exactly like he said.

I've been able to replicate the problem, but it seems to only affect the one volume that we recently migrated to a new storage array. The migration method was pretty simple:

1. Create the new LUN, format it, give it a drive letter, and add it to the target resource.
2. Use robocopy to mirror the data to the new LUN
3. Use it again to capture the changed data
4. In Failover Manager I performed some 3-card-monty to get the drive-letters swapped
5. I ran a powershell script I wrote to copy the directory-quota data

That all seemed to work. But now this has come up. Something has gone deeply weird here, and I'm looking for suggestions.

Edit RE: Offline files
Changing the offline files to disabled on my station causes everything to show up normally (where in this case normal is "as Win7 sees the world"), with the formerly XP-only files just gone. However, on another admins station, he still can't make the Win7 files appear. This is closer! But it does raise the question of lost-data.