Exception when trying to use brushes from "Brush collection" plugin

[Fabian42]

I'm using Debian 9.11, where only Pinta 1.6 is available. The plugin refused to be installed in it and demanded Pinta 1.7, so I installed the latest development version from the website, which was the Windows version of Pinta. It ran fine with Mono (4.6.2.7) and I was able to install the plugin. However, every time I try to use a brush from the "Brush collection" plugin, Pinta shows an error popup and an error message appears in the console (if I run Pinta in it). Here is the full log from one time where I simply opened Pinta, clicked on the brush type menu, selected "Inteligent erase" (nice typo BTW), clicked on empty space of the image, closed the error popup with "OK" and quickly closed Pinta with Alt+F4 (because otherwise it keeps opening error popups):

fabian@fabian:~/Downloads/pinta-dev-1.7.0.236$ mono Pinta.exe
Marshaling button_press_event signal
Pinta: System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.MissingMethodException: Method 'Pinta.Core.ColorBgra.ToStraightAlpha' not found.
  at Pinta.Core.BasePaintBrush.DoMouseMove (Cairo.Context g, Cairo.Color strokeColor, Cairo.ImageSurface surface, System.Int32 x, System.Int32 y, System.Int32 lastX, System.Int32 lastY) [0x00000] in <aaffe1d6dd2445ac9d84c55429a1e1ad>:0 
  at Pinta.Tools.PaintBrushTool.OnMouseMove (System.Object o, Gtk.MotionNotifyEventArgs args, Cairo.PointD point) [0x001b0] in <1bd539a0205d4620a1e6a171cec01b87>:0 
  at Pinta.Tools.BaseBrushTool.OnMouseDown (Gtk.DrawingArea canvas, Gtk.ButtonPressEventArgs args, Cairo.PointD point) [0x00046] in <1bd539a0205d4620a1e6a171cec01b87>:0 
  at Pinta.Tools.PaintBrushTool.OnMouseDown (Gtk.DrawingArea canvas, Gtk.ButtonPressEventArgs args, Cairo.PointD point) [0x00000] in <1bd539a0205d4620a1e6a171cec01b87>:0 
  at Pinta.Core.BaseTool.DoMouseDown (Gtk.DrawingArea canvas, Gtk.ButtonPressEventArgs args, Cairo.PointD point) [0x0002f] in <aaffe1d6dd2445ac9d84c55429a1e1ad>:0 
  at Pinta.Gui.Widgets.PintaCanvas+<PintaCanvas>c__AnonStorey9.<>m__13 (System.Object sender, Gtk.ButtonPressEventArgs e) [0x0005c] in <02a802d61efa4842b1cf8e4c2ce719cb>: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, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00038] in <8f2c484307284b51944a1a13a14c0266>:0 
   --- End of inner exception stack trace ---
  at System.Reflection.MonoMethod.Invoke (System.Object obj, System.Reflection.BindingFlags invokeAttr, System.Reflection.Binder binder, System.Object[] parameters, System.Globalization.CultureInfo culture) [0x00053] in <8f2c484307284b51944a1a13a14c0266>:0 
  at System.Reflection.MethodBase.Invoke (System.Object obj, System.Object[] parameters) [0x00000] in <8f2c484307284b51944a1a13a14c0266>:0 
  at System.Delegate.DynamicInvokeImpl (System.Object[] args) [0x0010d] in <8f2c484307284b51944a1a13a14c0266>:0 
  at System.MulticastDelegate.DynamicInvokeImpl (System.Object[] args) [0x0000b] in <8f2c484307284b51944a1a13a14c0266>:0 
  at System.Delegate.DynamicInvoke (System.Object[] args) [0x00000] in <8f2c484307284b51944a1a13a14c0266>:0 
  at GLib.Signal.ClosureInvokedCB (System.Object o, GLib.ClosureInvokedArgs args) [0x0006d] in <5a439e0caae7469886e7119d9f6bc621>:0 
  at GLib.SignalClosure.Invoke (GLib.ClosureInvokedArgs args) [0x0000c] in <5a439e0caae7469886e7119d9f6bc621>:0 
  at GLib.SignalClosure.MarshalCallback (System.IntPtr raw_closure, System.IntPtr return_val, System.UInt32 n_param_vals, System.IntPtr param_values, System.IntPtr invocation_hint, System.IntPtr marshal_data) [0x0012e] in <5a439e0caae7469886e7119d9f6bc621>:0 

The same happens with other brushes from this plugin, even the stacktrace is exactly identical.