This is a common problem with samsung tv's and universal & oem remotes. The problem is the samsung preset code is using the wrong protocol, at one time it was the right one but samsung changed it. Unless theres a preset code with the corrected protocol, the preset codes will not give you repeating volume commands.

As you wrote, your original samsung tv remotes works fine, the Sony vl900 is a learning remote, use the samsung tv remote to teach the vl900 the proper volume commands.

Universal remotes like the Radio shack 15-133, 15-134, or 15-135 have a preset code with proper protocol, the tv code is 10702.