Although I have listened some songs hundred of times I can't sing the lyrics to any of these songs from beginning to end without pauses. However I am able to whistle the whole song without difficulty.
It seems other people are complaining about this annoying condition as well. This particular answer claims it is quite likely related to the interhemispheric communication:
I also find that when I take the supplement piracetam, my ability improves. (It has in fact improved over time anyway)
Piracetam has something to do with interhemispheric communication.
Any answers for what causes this condition?