SD card limits or diagnostics?

[upstatealbundy]

This weekend I finally got up the courage to root my DX & install Liberty3 v2.0. To do so, I had to upgrade my µSD card from the standard-issue 2GB, so I bought a PNY Class 10 16GB card. I formatted the card through the phone before flashing the ROM.

After the first couple hours honeymoon period, I started noticing some apps not working right, and a little flakiness overall. The most common issue seemed to be trouble writing to the SD card from SwiftKey X (updating language packs), Evernote (syncing my notes from the server) and downloading apps in the Amazon Appstore.

After backing up my data, I reformatted the card agin, put the data back, and the problems continued immediately. Since Evernote was the most reliably broken, I deleted the whole directory from the card & had the app re-create everything. Problems continued. I reformatted again and still no improvement.

Desperate, I switched back to the original 2GB card last night and the phone & apps have been rock-solid ever since.

I've run a chkdsk on the card (via USB cable, phone in USB Storage mode) from Win XP, and it found no errors.

The spec sheet says the phone can take up to a 32GB card, so size shouldn't be a problem. How else can I attempt a diagnosis of this card? I have a 16GB Class 2 coming this weekend that I can borrow for testing, but would prefer to get a more conclusive test proving that the card is bad before I return it to the store and possibly get an exact replacement which may or may not do the same thing (assuming it's a compatibility issue and not a bad card). I've been warned that this Class 2 is "really slow" but any port in a storm - I'll take slow over unreliable.