We have encountered a subtle issue with ExtJS grid.
It is quite regular grid with standard 'cell editor' plugin and two editable columns (having at least two is important).
Once an editable cell is submitted, the store backing the grid gets reloaded.
However grid reload takes place in a subsequent time slot because it's a part of asynchronous task completion.


All this works well unless the user submits editable cell with the Tab key rather than with Enter. Tab makes second column's cell editor visible and shifts input focus there. After that the store reloads, or at least I believe it happens afterwards.


At first glance nothing bad happens to the UI, it continues working as usual. However after some time an attempt to hover the mouse over any element to which a tooltip is attached causes crash and console gets flooded with errors.


We've been able to establish immediate reason of this: garbage collection cycle that follows grid reload treats the input field belonging to the second column's editor as garbage. As a result `Ext.Element` instance wrapping this field has its `dom` property erased. By itself it's seemingly not an issue. However, for some reason, when it comes to show a tooltip, the system tries to get its hands on the `Element` that was previously garbage collected. Strangely enough, that element has nothing to do with tooltips.


In order to reproduce this open the fiddle(https://fiddle.sencha.com/#fiddle/338q) and then
- Double-click any cell in the first column to make it editable
- Type any value
- Press Tab on the keyboard
- Wait 30 seconds
- Move and hover the mouse over the grid cells to view tooltips


It does not need to be a grid tooltip, the bug equally occurs even if the mouse hovering over any unrelated UI element with tooltips.


So the question is: how can it be that garbage-collected element is reused, and how to correct this?