Losing changes from the current session when camping to yourself is a known issue. The UI is triggered to load newly saved settings whenever the character's name changes. When you camp to yourself the name doesn't change, so you get the original settings you had when you first logged in. If you need to log back in to a character without shutting down the game, the easiest thing is to log over to Character B then back to Character A as you mentioned. Otherwise you can do a /loadui from Character A, but you will need to zone once to fix some inconsistencies caused by the /loadui.
You can override the default Experience progressbar width by opening eq2ui_mainhud_experience.xml and changing the value at BarWidth near the top of the file. Any characters that have not made a change to this setting will get the width that you set.
Code:
<Data Name="1" Tag="BarWidth" Value="440" />
.