After some tests, I have found that the option "Automatically format the XML edited by the visual layout editor" (in Preferences | Android | Editors) might be the culprit here.
With my tests, I've found that changing a property (such as the layout_gravity) while in Graphical Layout design mode always screw up the visual display of the file when I go back to the XML (text) mode when this option is ON but that I have no problem when it's off.
If you want to format the XML upon your return from the Graphical Layout design mode, simply use the shortcut Ctrl-Shift-F. Also, I didn't see any problem with using the option "Format on Save"; even when I use it in the Graphical Layout mode; so you can use Ctrl-S instead while you're still in the Graphical Layout mode to both save and format your XML.
I've tried other editors options like "Show range indicator" or "Use characters to show changes in vertical ruler" but I didn't see any difference in behavior with activating or de-activating these options.
Finally, to correct the visual display of the file when it's corrupt; I found that using the shortcut: Ctrl-A, Ctrl-C, Ctrl-V is a little easier than closing/reopening the file. This is equivalent to making a Select All, Copy, Paste; effectively copying the whole XML file over itself.
