It looks like there are two issues:
1) The flyout panel background is missing. When you select an object, a gray "flyout" panel should appear with all the action blocks for the selected object. In your screen shot, the blocks are visible, but not the gray background. Related to this, the background for sockets is missing. Please see this comparison: https://www.screencast.com/t/M0gw2iRHG
We've found the cause. Very strange - it's related to your Dutch keyboard setting. We're working on a solution and will get back to you about this.
2) You said: "Deleted objects won't let me remove their control blocks" I'm not sure I understand the issue. When you delete an object on the page, SmartBuilder does not automatically delete action blocks related to the object. This is done on purpose because often authors want to keep the action and just switch the reference to a different object. You can delete the "zombie" blocks by selecting them with your mouse and using your keyboard delete key. We no longer have the trash can
It was fun, but caused some problems. If I'm misunderstanding this issue, please let me know.