This problem is sometimes seen with Arboretum and other 3rd party plugins. If you adjust parameters on a plugin and close it, it stays as you set it. If you reopen the same plugin, it's parameters have been reset.

The solution is to "tweak" the plugin the way you like it, then save those settings as a preset in the plugin's mini-menu. If you have to reopen the plugin, simply recall the preset you just saved.

A solution is being worked on for future releases.