It might be related to bug 1370274. It can happens often that both cell highlighters and infobars are still visible once we left the cell area in the grid outline. That seems because more and more we over the grid ouline, more slow it becomes. STR: 1. Open a page with a simple grid (e.g. https://gridbyexample.com/examples/code/example1.html) 2. Enabled the grid highlighter and grid outline from the layout panel 3. Quickly move the mouse over the grid's cell in the grid outline. 4. Leave quickly the layout's panel area In more than few cases, at the step 4 there is a cell that is still highlighted in the page, with both infobars visible.
I investigated a little bit. When a mouseover event occurs, we debounce the cell highlighting, which means that it takes a bit of time for it to actually occur. So if you move very quickly, you may trigger a mouseout *before* the cell gets highlighted. So that means it will get highlighted and never un-highlighted, because the mouseout already occurred. Matteo is adding debouncing for mouseout too in bug 1370274 which might fix this bug, so we better block on that one.
It's indeed seems fixed by patch of bug 1370274. Thanks for looking into it Patrick!