I cannot drag & drop mp3s from my Windows Explorer into my playlist v.5.6

[Moshka]

I could previously drag any music file directly from my Windows Explorer (Win 7) and into my Winamps playlist. Two days ago I noticed that for some unknown reason whenever I clicked twice on a song in the playlist, a pop-up dialog prompting me to add the file to the playlist appeared. Being that I couldn't find how to modify that behaviour in the Preferences section, I installed ver. 5.601 half an hour ago. Oddly, now I cannot drag and drop from the Explorer. I can drag songs which are shown inside my Media Library, though, but I use the other function a lot. I looked inside the Preferences again, but nothing rang a bell.

Is this a known bug? If not, any hints as to how to fix this?