It sounds like you have a relative/single-turn encoder instead of an absolute/multi-turn encoder. What's the type code of the motor connected to the drive? A Bosch-Rexroth motor type-code should have an indication of the encoder type.
A relative/single-turn encoder requires re-homing after power cycles or going to parameter mode. A relative/single-turn encoder does not keep track of the position over multiple turns, so when the drive is powered off or has entered parameter mode, the drive can't be sure that the encoder didn't move while it wasn't monitoring. An absolute encoder reports its actual position to the drive over many turns of the encoder. After losing power or entering parameter mode with an absolute encoder, the drive can trust the encoder position and knows if it has moved.
From the IndraWorks help file (General information on establishing the position data reference) . "The position data reference of a relative measuring system to the axis has to be re-established each time the drive is switched on or after the position data reference is lost (switching to PM). For this it is necessary to move to a defined axis position and set the actual position value to an axis-related value in a defined position."
