Developer Ailsa Investments, an offshoot of major property firm Meyer Bergman, wants to get hold of the architect's designs for the £35 million Trinity Park House development in Edinburgh.
But Murphy is refusing to hand over the project's plans, claiming he is entitled to use them whenever he wants.
Now Ailsa - at one time Murphy's client alongside Scottish housebuilder CALA - has launched a High Court action to contest the architect's position.
The firm, based in Belfast, is suing the high-profile Edinburgh designer for breach of contract.
The dispute is the latest in a long line of hiccups to have blighted the project, which was granted planning permission by Edinburgh City Council last July.
Demolition of an existing office block and work on the new scheme was originally earmarked to begin at the beginning of 2006 but has stalled, due to the current court case.
Local opposition prompted a substantial redesign of the scheme - which includes 300 flats in a northern district of the Scottish capital - in early 2005.
Murphy is known to be particularly proud of the project, which employs underground parking to maximise space and substantial landscaping, but the source of the current dispute is still unclear.
The case is the second High Court dispute over copyright in the last two weeks to be revealed by the AJ.
KSS Design Group is currently in a wrangle with developer Bacassa over ownership of the designs of a leisure project in Barbados (AJ 23.03.06).
Here, the two parties are locked in a legal dispute over fees. KSS has been fighting to win what it believes are unpaid bills from the developer.
Ailsa's action is being handled by the Edinburgh office of solicitor Shepherd and Wedderburn.