HTC EVO 4G : Downloading MMS Failed / Old Text Messages Reappearing?

Asking a question for my father in law who is having problems with his EVO (I have an EVO but can't replicate this problem to help).

During the past week, the EVO with the problem was not downloading MMS messages onto the phone. The download process would start but would result in an error that said something like "generic network failure." We thought it was a temporary network connection issue. This started with the stock "Messaging" app installed on the EVO.

What then happened is VERY ODD. All of a sudden literally HUNDREDS of old previously deleted messages dating back to June of this year (yes, it is now NOVEMBER) were being downloaded and loaded into the messaging app. This happened not only with the thread that could not receive the recent MMS message but essentially ALL THREADS from whomever might have contacted my father in law since June! This happened once, we totally cleared out the messaging app threads and even deleted the cache information and data through the Manage Applications options on the phone and, once again, receipt of a few current messages would again trigger this FLOOD of text message data from MONTHS ago!!

Has anyone heard of this problem? It seems to me to be related to the Sprint Network because there should be no remnants of any of the old text messages once deleted from the phone itself. We went to a local Sprint store this morning and even did a hard reset BUT upon testing the text apps again, the problem recurred!

This problem occurred first with the stock Messaging app and, thinking that the Messaging app was the problem, we installed ChompSMS with the hope of fixing the issue but the problem occurred with Chomp as well.

Again, I am posting this for my father in law's EVO...I have an EVO too, running ChompSMS with NO PROBLEMS...matter of fact I have NEVER heard of or seen this issue with many-month-old text REAPPEARING on the phone. Any suggestions or thoughts?