I really hated PGAdmin 4 at first because it was so broken compared to PGAdmin 3, but now it has progressed to the level that it is really quite usable, and I congratulate all of the developers for their hard work! I see people complain about the tool, but I would like to give praise for the work that has been done. I am a developer, so I know how hard it is to implement something as complex as PGAdmin.
There is still one feature that PGAdmin 3 had that I really miss. In 3, I could edit a table and select a row and 'copy' it, then in a second table, I could select the empty row at the end of the table and paste, which was an easy way to insert a missing row from possibly a development Database to the Production one, for example.
There is also one really problematic issue when using Safari on a Mac, I don't know if it affects other browsers as opening a PGAdmin window on a Mac always opens in Safari (I think it might be able to be changed, but I am OK with it as it is). The issue is that one can 'detach' the window into a floating window, but there is no means to put it back! In earlier releases, it used to save the detached window configuration somehow, and from then on, the window was forever a floating window. I believe this has been fixed, because the last time I accidentally detached the window, I simply closed it and opened a new one and it was again part of the active frame. In any case, this is a real annoyance, and I can find no way to undo the detachment other than closing the windows and starting over.
Yes this is an issue. The problem is with the underlying library which is used for docking/undocking. Until we figure out the solution, there is workaround for it. You could dock back single tabs one by one. Other solution would be to use File->Reset layout. Please note, this would reset the complete pgAdmin layout to defaults.