I looked at this issue again.
With Code::Blocks v17, when you hit the enter key in the editor, it creates a new line of course, and then the symbols browser automatically regenerates. This is obvious since the browser window starts a redraw, it shows the topmost entries again.
With Code::Blocks SVN, when you hit the enter key in the editor, the symbols browser does not respond to it. When you save your file with added lines, no response either. So that is why it gets out of sync. Logically only the parts above the newly added lines are still synched properly.
Edit:
More recent Win32 builds by Xaviou, like rev12990:
Same issue (also: malfunctioning alpha channels of toolbar icons)
My own Win32 build of rev12991 SVN with wxWidgets v3.2.1:
Same issue (also: malfunctioning alpha channels of toolbar icons)
cb_output31_64-2020-11-22.zip on Windows 7 x64:
Same issue. This is a very early symbols-browser reimplementation
CB_20221022_rev12990_win64 on Windows 7 x64:
Same issue. But less prone to crashing because of it, compared to the other three.