They can be properly positioned in the score, yet change their placement by themselves in the parts when parts are generated. This may have something to do with the staff reduction, or certain fixed measurement units (the distances SHOULD scale along with the staff, don't you think?) but there is no predicting how one of these is going to look in the parts.
When a repeat text occurs on the last bar of a multimeasure rest, its position cannot be changed by either the Selection Tool nor the Repeat Tool while in Page View. I have to go into Scroll View to adjust it, then switch back to Page View to see if it's in the right place. This lack of adjustability applies to repeat endings when there is a multimeasure rest in the ending, too.
There are other circumstances where the repeat texts move, but I don’t use repeat texts any more (I use non-playback Expressions instead) and so have stopped documenting their oddities.