The problem occurred for me when I un-docked the hierarchy panel and it transitioned to a new window. Testing in a blank project also created the problem.
I was able to reveal the panel tab again though in both projects by un-docking another panel (Palette for instance) and including it with the created window containing the un-docked hierarchy panel. Once the two were joined in the window, then I was able to click on the yellow triangle portion to reveal the previously hidden tab.
It may be that the unreal window icon was somehow interfering with the ability to click on the yellow triangle in windows with only a single panel.
Below is an image from the document page I linked in the opening topic that shows the yellow corner-tab I am talking about. This yellow corner-tab can reveal hidden panel tabs when clicked on. See the linked article for more details if necessary.
This problem may or may not be limited to UMG panels. I’ve only encountered it using UMG.
It occurs when a panel is un-docked from the editor (creating a stand alone window) and when the panel tab is subsequently hidden by the user. Once hidden, the yellow triangle seems to be blocked from the unreal icon preventing the user from being able to reveal the hidden tab, see below.
The work around I posted earlier was to un-dock another panel and merge it to the left side of the newly created window. This results in panel shifting over to the right, away from the unreal icon, and subsequently permitting the user to press on the yellow corner tab to reveal the hidden panel tab.
We checked a number of different settings and have not been able to reproduce this on our end at all. Have you made sure that you are hoovering directly over the yellow tab and not just beside it?
I am certain that I have tried clicking on the yellow tab in multiple locations on the triangle during the problem situation (seemingly hidden behind the Unreal logo as displayed in the image I linked). The results from the click attempts are:
-During single clicks nothing seems to happen.
-During multiple clicks (at least a few in immediate succession) it will close the panel altogether. The panel then must be restored by using the window menu.
-Clicking just below & right of the yellow tab on the U icon provides the menu for “restore”, “move”, “size”, “minimize”, “maximize”, “close”.
I’m assuming that your attempts to reproduce the error on your end were as I detailed on the response with the included images? In summary;
(1) Un-dock a panel to create new window
(2) Hide the panel tab on the un-docked window with right click hide
(3) Attempt to restore tab by left mouse button click on yellow triangle in top left corner (at this point it should look exactly as I have indicated in the blocked image provided)
I am not sure if it will be helpful, but I experience the same problem with viewports (Window->Viewports->…). Each time I undock the viewport and hide the tab the yellow triangle in upper left corner which should normally restore tab is not responding. I can resize the window, but i cannot dock it to main gui because of this bug. I use 4.6.1 on linux (Linux heka 3.11.10-25-desktop #1 SMP PREEMPT Wed Dec 17 17:57:03 UTC 2014 (8210f77) x86_64 x86_64 x86_64 GNU/Linux).
This bug is from a much earlier version of the editor, and as such many changes have occurred. Please make a new post describing the error you are experiencing along with what steps I can take to reproduce this on my end.