ID 422495 - The interface becomes laggy and sometimes non-responsive when cycling the Channels/Layers with the arrow keys

Problem summary
The interface becomes laggy and sometimes non-responsive when cycling the Channels/Layers with the arrow keys.

Customer reported version
mari.4.2v2

Customer reported platform
centos7

Steps to reproduce

1) In Mari, open any project or create a new one.

2) Open the Layers palette and have at least 10 layers of any type available.

3) Select a layer and hover the mouse near the edge to refrain from tooltips.

4) Use the up/down arrow keys to cycle rapidly between the layers in the Layers palette.

5) Observer the layer UI with the rapidness of the switching between layers.

Expected behavior
The UI should appear fluid and dynamic with no signs of slowness or delay.

Actual behavior
Cycling the Layers or Channels palette creates a slowness and lags after consistent use. This lag is also common when selecting Channel or Layer Blend modes.

Workaround
Selecting the top layer and opening the context menu (right-click the layer item), and choosing Caching > Cache Up To Here seems to correct the issue in versions 4.5v1 and up.

Reproduced by Support in

Mari 4.6v1 - Windows 10, CentOS 7

Mari 4.5v2 - Windows 10

Mari 4.5v1 - Windows 10

Mari 4.2v2 - Windows 10

Mari 4.1v1 - Windows 10, CentOS 7

Unable to reproduce bug in:

Mari 4.0v4 - Windows 10, CentOS 7

Earliest version tested
Mari 4.0v4 - This issue doesn't appear in this version and has regressed