According to the 4th Dimension Language Reference and Macintosh Human Interface Guide, a borderless window is supposed to be Modal. "Modal" means the user can perform no other actions until the dialog is dismissed. In version 6.0 and 6.5 of 4th Dimension, Type 2 Windows broke this rule. This has been fixed in 4th Dimension 6.7 to match the manual and guidelines.
You may want to consider using a Floating Plain or Alternate dialog box (Type -2 or -3) instead of a Modal Dialog if you wish to allow the user to perform other operations in your program while the dialog is displayed (such as making a selection from a floating palette).
However, if you really want to have a borderless, non-modal window you can use Type 35.