Main display page had become undocked

I am having a difficult time understanding what you are describing. Is this similar to what you are seeing but you want to have the left side with the accounts in a smaller view and to show the right side for the register being a larger view? If this is the case, then you can change the location of the divider line to accomplish this as noted in this picture.

If this is not the issue you are trying to describe, would you be able to take a screen shot of what you are seeing, edit it to remove or hide personal or confidential information, save it as a picture file and then click and drag that picture file to "Leave a Comment" with any additional information you think might be helpful?

Edit > Preferences > Register

Un-check "Use pop-up registers"

I'm glad that it worked for you. In answer to your question: I am not aware of any way to lock the sizing of each section nor am I aware of a "standard" size. What should happen is that when you close Quicken it should remember your last setting of it so when you open it the next time it will be as it was the last time.

I don't know why it happened to you but I know that for me sometimes there is something in my computer that will cause a sudden spike in use of my computer's memory or CPU. When that happens and when I am moving the cursor sometimes the cursor will "grab" things on the screen and move them. Sometimes it is words, sometimes it is the entire screen of an application and sometimes it can move a view in the screen. In Excel, Word and Acrobat it will sometimes "grab" the screen as a magnifier and increase or decrease the magnification. The "grabs" don't last long…usually less than 1 second…but that is enough time to cause some undesirable things to happen. Maybe something like that is what happened with your system.