Sorry for bad english, i'm from Ukraine.
So, if i press Ctrl + C buttons, or Quit from application - i have bug, and i can't exit, only htop + SIGKILL can help.
Debian 8 Jessie, testing, x86_64, I check stable and testing version of Pinta - i have bug anyway.
I try install from apt-get (debian repo), from u'r site, and from source. Anyway I have bug.
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.ArgumentNullException: Argument cannot be null.
Parameter name: src
at (wrapper managed-to-native) System.Runtime.InteropServices.Marshal:copy_from_unmanaged (intptr,int,System.Array,int)
at System.Runtime.InteropServices.Marshal.Copy (IntPtr source, System.Byte[] destination, Int32 startIndex, Int32 length) [0x00000] in <filename unknown>:0
at Cairo.ImageSurface.get_Data () [0x00000] in <filename unknown>:0
at Pinta.Core.CairoExtensions.ToPixbuf (Cairo.ImageSurface surfSource) [0x00000] in <filename unknown>:0
at Pinta.Core.EditActions.HandlerPintaCoreActionsEditCopyActivated (System.Object sender, System.EventArgs e) [0x00000] in <filename unknown>:0
at (wrapper managed-to-native) System.Reflection.MonoMethod:InternalInvoke (System.Reflection.MonoMethod,object,object[],System.Exception&)
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
--- End of inner exception stack trace ---
at System.Reflection.MonoMethod.Invoke (System.Object obj, BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00000] in <filename unknown>:0
at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <filename unknown>:0
at System.Delegate.DynamicInvokeImpl (System.Object[] args) [0x00000] in <filename unknown>:0
at System.MulticastDelegate.DynamicInvokeImpl (System.Object[] args) [0x00000] in <filename unknown>:0
at System.Delegate.DynamicInvoke (System.Object[] args) [0x00000] in <filename unknown>:0
at GLib.Signal.ClosureInvokedCB (System.Object o, GLib.ClosureInvokedArgs args) [0x00000] in <filename unknown>:0
at GLib.SignalClosure.Invoke (GLib.ClosureInvokedArgs args) [0x00000] in <filename unknown>:0
at GLib.SignalClosure.MarshalCallback (IntPtr raw_closure, IntPtr return_val, UInt32 n_param_vals, IntPtr param_values, IntPtr invocation_hint, IntPtr marshal_data) [0x00000] in <filename unknown>:0
Which Pinta version were you using?