From the article here:
Ъ - Boeing упал чисто по-человечески
I will translate only the most relevant portions:
The crew of Boeing, according to some experts, was in a critical situation, after the aircraft, which was lead by controller, after safely performing four turns in the "box" and taking a course for landing, suddenly climbed sharply. This maneuver, the cause of which has not yet been determined, apparently, was a complete surprise to the controller of Perm airport Irek Bikbov, who called these actions inadequate for the pilots themselves. What follows from decoding of talks among the pilots, they learned that the machine is going up from the radio dispatcher. The climb itself (rather than descent) was not particularly dangerous, especially since the controller suggested that Boeing pilots turn and repeat the approach. However, they were unable to comply with his instructions for yet undetermined reasons.
It is likely that the incident simply confused them and they lost spatial orientation. In any case, this is evident in their [pilots]conversation - after accepting controllers instructions for second approach, pilots began to vigorously argue about turn direction - left or right. The captain, who insisted on the left turn, won this dispute and the aircraft turned away from the landing "boxe" on the right, and towards residential areas of Perm. However, the crew was unable to complete this maneuver: the plane banked too far to the left and fell into a rapid spiral dive.
While the article does not specifically says so, it appears as though they had access to cockpit voice recording.
They go on to speculate about differences in artificial horizon output between Russian and foreign planes that may have contributed to this, as well as relative inexperience of pilots with this type of plane (captain had a few hundred hours as an FO on Boeing, prior to that FO on Tu-134, etc).
Who knows what that means, but Kommersant is generally a fairly respectable publication.