Designer bug? - column properties box

Hello, I am working with 6.5.1 designer.In any mail template view with more than one languaje pack, I go to some column, clic properties and … I have to wait betwen 5 to 9 minutes to see any information in properties box!!!

I need to change more than 100 columns and this behavior is totally unacceptable.

Some help?

Thank you in advance and sorry for my english.