This situation can happen because it generates some blocking.. i forgot the details, but it has to do with the RXLEV of the UL and DL.
Nevermind. I think you can solve the problem by activating both DL and UL power control. And if they are already activated, try decrease by few dB’s all the PC thresholds.
For instance : UL PC : Up = -85dBm, Low = -95dBm
DL PC : Up = -75dBm, Low = -85dBm
And don’t forget the MIN POWER for MS (2dBm) and the BTS (min power possible ? depends on your BTS’s brand)
Hope it helps.. Please let me know how it turns out !