You may have noticed this too. When you create a template, the Base Template dropdown may be tricky to operate with. If you are trying to find a template in the subfolders to inherit from and miss the expansion plus, the tree will collapse and you will have to start over. This has been bugging me for a while so I asked the tech support if there is an easy way to fix this and not have the tree to collapse.
Luckily, there is an easy fix, but you will have to mess with the Sitecore.js file located under /sitecore/shell/controls.

What you need to do is to add a global variable in Sitecore.js:

var iAmTree = null;

Then straight after line 563 within scSitecore.prototype.postEvent = function(tag, evt, parameters) add the following:

iAmTree = false; 
if (ctl.className.toString() == "scTreeItem") iAmTree = true; 

And finally within scRequest.prototype.resume = function() alter this IF statement:

if (this.closePopups && typeof(scForm) != "undefined") {

to this:

if (this.closePopups && typeof(scForm) != "undefined" && iAmTree != true) {

This will also affect the Droptree field’s behavior and possibly more areas.

And you may have guessed – create a backup of Sitecore.js file and use the solution on your own risk ;-)

Special thanks goes to Ruslan for providing the fix.