System Information
Intel i7 8750H, 16GB DDR4, GTX1060
Operating system:
Windows 10x64 PRO
Graphics card:
GTX1060

Blender Version
Broken: 2.82 0c57373e2c46
Mesh will animate past the mask KeyFrame Point. But the simulation follows rules of as if the mask didnt clip the centre.
Broken: 2.79 e045fe53f1b0
Works better then 2.79, the mesh will animate until the mask is Keyframed Frame

Short description of error
I am not seeing the MASK Modifier have proper effect of the cloth simulation.

Exact steps for others to reproduce the error
Open Blender

1. reduce size of cube by 75%
2. Scale Cube along Y azxis to entire width of viewport
3. Edit mode and "Control R" to add edges Add 100 edges from centre
4. using Face Mode editing, Select two Outer Edges only. and create a Vertice Group and assign them 100% shading
5. select the most using Wireframe view mode, Ctrl B and select only the most centre box and assign to vertice group 2. (this is the part that I want to have removed using MASK)
6. Set the Animation frames to max 100 frames (not the standard 250) so we are animating 1-100
7. add a Mask Modifier and ensure its top of modifiers list, add vertice group 2 and invert it.
8. Add Cloth and pin Vertice Group 1,

now keyframe the Mask Modifier to remove the centre of the of the long cube from frame 50 onwards. so frames 1-49 show the entire cube
frames 50-100 show the cube with the centre missing..

I am expecting that the simulation should....
Cloth should animate the cube to Bow downwards in center, and after frame 50, let go and drop down after the bowing of the cube.

but it using Blender2.82 it seems to follow the path as if the mask has been applied the entire time..

I have a blend file created in 2.79.. but also works in 2.82, to save you rercreating my steps..

https://drive.google.com/open?id=1l-w2gBIPpAfFvokqr2ouIaHSbAcFFR0x

Regards
Shaun