Microsoft confirmed faulty Yahoo Mail synchronisation as the cause of the so-called phantom data consumption some users of Windows Phone 7 smartphones had experienced.
The announcement came just hours after Within Windows' hacker Rafael Rivera published evidence that the Yahoo Mail synchronisation was the cause of the issue.
"What I discovered was shocking, although not surprising. Yahoo’s IMAP server does not respond to FETCH requests correctly," Rivera said in a blog post. "Yahoo is sending ~25 times as much data as it needs to."
Microsoft belatedly confirmed the issue, saying: "We have determined that an inefficiency exists in the synchronization of email between the Windows Phone Mail client and Yahoo! Mail."
"This inefficiency can result in larger than expected data usage for a very small percentage of users. Microsoft and Yahoo! have worked together to identify a fix, which will be rolled out in the coming weeks."
In the mean time Microsoft described a work around to avoid the problem which can be found on the full Microsoft statement at Windowsphonesecrets.com.
Windows guru Paul Thurrott blasted Microsoft for the delay in releasing the information, saying "there’s no reason, and no excuse, for this information to not have been provided earlier."
Microsoft conspicuously did not address why the excessive Yahoo Mail data use would come out of user's 3G allowance even when Wi-Fi is available, something Thurrott claimed was a bug in Windows Phone 7.