From memory JBuilder did have issues with its GUI builder.
Code emitted JBuilder's tools was not isolated from other code that was written for the application. It was easy to add a line of code that would make the included builder tool to not show the resultant GUI correctly.
This was from JBuilder 9 and JBuilder 2006, other than that issue it was a really nice IDE to use.
BTW, I used JBuilder extensively. What a topnotch tool from Borland. Pity they didn't survive the virulent competition during those IDE wars period. I still remember settling an argument with a colleague about his insistence to use the newly arrived Netbeans, while I fired up my JBuilder IDE (Yellow Porsche splash screen IIRC), created a gui, added jdbc data controls, coded a few lines and hit compile - ALL while his Netbeans was still loading with that dastardly progress bar.
(These comments have been much needed catharsis for me.)