Say a lawsuit has been filed with a court. A judge looks at the case and makes some initial directions (e.g. requests formal written statements, considers case management memoranda filed by the parties, directs for amicus curiae to be appointed etc.).
Then, as the case proceeds, it suddenly happens to be in the hands of another judge: the court just changes judges without giving a reason.
Is this something that courts are allowed to do as they please? Should not a case, where possible, be done by the same judge? Should not changing judges be allowed only for a good reason e.g. unavailability of the original judge? Should a judge change be an alarm for the parties? Can the parties question the court as to why the judge was changed?
Answers re any jurisdiction are welcome, though particularly interested in New Zealand.