T46G losing DSS Key programming (partial)

[Cory]

We have recently made the decision to switch to digital phone service, and our provider (Vonage) sold us twenty-six T46G phones as part of our package. Our porting is happening today and Monday, so we just started setting up phones this week.

I've spent the last 2-3 days programming the DSS Keys for each user via IP from my web browser.

Two days ago, one user lost partial programming of her DSS keys. The Type was changed back to "Line" from "Speed Dial" or other settings for many (but not all) of her DSS Keys, the Values were blanked out (numbers erased), but the Labels were left alone.
So, on the phone, it looked at first glance, everything was fine... but most of the DSS Keys didn't function as they were programmed (because part of their settings are erased or set back to default).

I re-programmed her phone yesterday, but it lost the same programming again today... along with 4 other T46G phones... same type of partial erasure/loss of DSS Key programming.

Vonage recommended I upgrade the firmware with an image from Yealink's site. I downloaded the T46-28.81.0.25 firmware... and I've pushed it to 5 phones using the procedure found in the Yealink documentation.
3 of the phones upgraded properly, but 2 of the phones kept updating and rebooting for about 20 minutes, and eventually ending up with "No Service". They're on the network, with an IP address, but I cannot log into them using either the default Yealink credentials or my Vonage credentials. Also, the firmware shows to be 28.81.193.15. This firmware is beyond what I downloaded and pushed to the phones... it's like the phones downloaded their own firmware after I pushed the image I downloaded from Yealink.

What can I do, since I cannot log into the phones to configure anything? They won't let me log into the phones via browser or directly at the handset.

Is this a firmware issue or something simple? Are the phones defective? I couldn't find any reports of similar issues.
Please, help... management is not happy, and I have to find a solution.