Yes, it's a Ram issue related. Probably you are on .290 and on that FW this is a known problem when you try to go back to the application from multitasking menu. A Ram problem was fixed on .136, this is what many users reported but I am not sure. What i know there is no any solution at the moment.
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My Evolution: Sony Xperia Z1 - UB + 4.3 Rooted + Deodexed, HTC HD2, HTC Diamond 2, HTC HD Blackstone, Nokia 7070 Prism, Qtek 9100, Nokia 3100, Motorola T720i, Nokia 3310, Sony Ericson PF 768 (Blue)
How Get Root on Sony Xperia Z1 with Locked Bootloader and the Latest Android 4.4