Thing to remember here is that with many IR remote systems, a command like volume has a code, a pulse train of course. However once the micro in the TV or whatever gets the code, ANY continued IR recieved will continue the operation. The remote does not repeat the pulse train, it just puts out bursts of IR at so many millisecond intervals.

This means that the TV might pick up just any stray IR and think you are still pressing the button.

Not all systems are like that but since it seems like it would be cheaper to implement, it's likely designed that way.

Sometimes you can test that theory by taking the right remote and a completely unrelated remote and hitting vol+ for example on the right remote and then hold down any key on the other remote. If the volume keeps going up, that's what you got.

In that case look for other sources of IR in the room, even sunlight reflecting off something, or in some kinda rare cases CCFL lighting. I know CCFLs are not supposed to put out IR but supposed to is a relative term. There was a thread on that not long ago but in that case apparently the CCFL interfered with the IR. While the IR output may be quite low, the reciever might be sensitive enough to take what it's got and misinterpret it.