Running Kubuntu 12.04 32bit (so awaiting the QT port with interest!) and Guayadeque from svn 3.5-1819.
When rearranging the layout by dragging and dropping a UI element, Guayadeque crashes every time if I release the element I'm moving when it touches the top, bottom or sides of the main window.

(gdb) run
Starting program: /usr/bin/guayadeque
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1".
...
The program 'guayadeque' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadWindow (invalid Window parameter)'.
(Details: serial 35664 error_code 3 request_code 18 minor_code 0)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the --sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)
[Thread 0xb3affb40 (LWP 25725) exited]
[Thread 0xb4e07b40 (LWP 25715) exited]
[Thread 0xb5891b40 (LWP 25714) exited]
[Inferior 1 (process 25709) exited with code 01]
(gdb) bt
No stack.
(gdb)

I tried running guayadeque with the --sync command line option as suggested in the above X Window error to try and get a meaningful backtrace and it wouldn't crash.