1) when I try to add a new folder for the bookmarks the program crashes (In 4.13 solved ensuring a "Default" folder.)
2) if I try to add a new folder even in 4.13 when there is the default folder, marble crashes.
3) if I open the bookmarks manager I can choose which bookmark folders to show (I added manually new folders in bookmarks.kml). When "checking"/"unchecking" them I can see the bookmarks appear/disappear but when I press "ok" all folders are "checked" and the all the bookmarks are shown.

Since I'm developing an application marble-based I have follow the problem through the code and I found out that the problem is one setting that is not handled by marble-qt settings dialog.
In fact, in ~/.config/KDE/Marble Virtual Globe.conf there is the following section:
[CloudSync]
enableSync=false
syncBackend=owncloud
syncBookmarks=true
syncRoutes=true
owncloudServer=
owncloudUsername=
owncloudPassword=

as you can see: "syncBookmarks=true" but there isn't any settings to access an ownClowd server. So I think it should be "syncBookmarks=false" by default. 
Maybe the same is for "syncRoutes". 
I changed the setting and there isn't any crash nor bookmark hide/show problem and there is no need to ensure a "Default" folder like the fix introduced in 4.13.

I suggest to introduce a synch configuration tab in marble-qt settings and disable bookmarks and routes sync by default.

Reproducible: Always

Steps to Reproduce:
1. add a new bookmark folder (program crashes)
2. since is not possible to add one folder in 4.12, add a new folder in the kml file
3. if you try to add another folder from marble interface the program will crash
4. re-open marble 
5. add one or more bookmarks
6. open the bookmark manager, uncheck the folder and press ok
5. the bookmarks are hidden and re-shown
Actual Results:  
1) the program has crashed
2) the bookmarks are shown instead to be hidden

Expected Results:  
1) the program must never crash
2) the bookmarks should be hidden

I am running marble-qt interface on:
1) kde 4.11.5 with QT 4.8 kubuntu 13.10 64 bit 
2) kde 4.12.4 with QT 4.8 slackware 64 bit current