Found it!
I’m copying this in here in case someone will ever look for the solution too.
About the Description Tag(s):
All iTunes tracks contain two description tags. In AppleScript parlance, these are description and long description. However, depending on the kind of track, only one of these description tags will be displayed in iTunes.
• TV Show or Podcast – Each of these types of tracks uses the long description. By clicking the “i” glyph in the track’s Description column a new window will display the entire text from this tag.
• Audio Tracks and Others – These types of tracks use the plain description tag. These tags do not have a “i” glyph and only hold 255 characters. Text from this tag can only be displayed in iTunes in its entirety by making the Description column as wide as possible.
However, as mentioned above, all tracks are able to use the long description tag field.
This script will enable you to view and update the long description tag of any track. Additionally, when using the script’s “Update” option (described below), the entered text will be copied to both tags. Thus you can provide long descriptions (greater than 255 characters of text) to any track to both the description and long description tags. And although only 255 characters will be visible in the Description column, the script can display the entire text from the long description tag.
http://dougscripts.com/itunes/
All credits to Doug!