A B757-200 Captain reports a dangerous practice implemented by his carrier; of issuing a Maintenance Release; even though maintenance had not even completed the reverser lockout procedures or required MEL checks 35-minutes later.

Narrative

Had reverser problem on airplane we were picking up at the gate. Maintenance advised us they were deferring the thrust reverser and locking it in the forward position. We were agreeable and got a new release from Dispatcher. Mechanic came to cockpit and told us not to touch hydraulic panel and left. We then got a new Maintenance Release over the printer. We called maintenance on radio to ask if they were done and they said no. 35 minutes later; Mechanic came to cockpit to do checks required by MEL. They had mechanics working on hydraulic parts; after we had gotten the Maintenance Release. Accordingly; I could have activated the hydraulic panel and pressurized what they were working on! This practice is dangerous! A new Maintenance Release means to me the mechanics are done; the checks are done; MEL complied with and the airplane is mine. I called on the radio to maintenance to ask about sending the Maintenance Release before the checks were done and he said they were almost done. Again; it was a full 35 minutes before they finished. Callback conversation with reporter revealed the following information: Reporter stated his carrier's practice of issuing an early Maintenance Release prior to mechanics finishing all their maintenance procedures and checks; is still continuing. He believes their Operations Manual requires all maintenance work is to be accomplished prior to issuing any Maintenance Release. With the Maintenance Release issued early and maintenance still working on the aircraft; no one knows for certain what the true system status of an aircraft is. Reporter stated he does not understand why this unsafe practice is allowed to continue.