Apple receives an unwelcome gift one week before Christmas: a class lawsuit with iPhone 5 and iPhone 5s users on AT&T's network as plaintiffs.

The claim states that the Cupertino-based tech giant knew and kept mum about a manufacturing defect in the iPhone 5 and 5s which directly affected AT&T clients.

The problem with the two handsets was that it forced users to tap deep into their mobile data, even when the devices had an active Wi-Fi connection.  

A number of iPhone 5 owners noticed the issue as early as September 2012, when their cellular data drained inexplicably fast. The lawsuit claims that consumers affected by the surge in cellular data consumption reached out to Apple and to their carriers to fix the problem.

The law firm Hagens Berman investigated the issue, as the class action complaint states [pdf].

According to the legal firm, the problem appeared when users streamed "high volumes of data" in an interval of 10 to 20 minutes. In the two new iPhone models, the graphics processing unit (GPU) was programmed to take care of all the stages of video display, namely decompression, decoding and showcasing content.

This meant that the Swift central processing unit (CPU) could be turned into "sleep" mode to save battery life, as it was no longer required for visual tasks. When the CPU entered sleep-mode, the Wi-Fi receiver shut down automatically, causing connectivity to fall back only on cellular signal.

Apple reacted to clients' feedback by releasing a fix for the bug, but sadly it only applied to Verizon subscribers. The carrier made clear that clients who stepped out of their data plan due to the bug would receive no cash penalties.

Hagens Berman found that Apple not only failed to release a fix for the AT&T customers, but it also refused to acknowledge the manufacturing defect. To summarize, the legal firm and plaintiff Thomas Palmer said that Apple was opaque in communication and ill-willed in action.

"By withholding this information and repair, consumers were unaware of the defect and were left to sort out high cellular data charges with their wireless carriers," Berman posted.

It should be noted that the issue plagued all devices running iOS 6 and iOS 7, and was finally resolved only in iOS 8.1.