There is a difference between "Breaking Change" and a "Bug". The difference is that the "Breaking Change" is done intentionally to provide better functionality, but since it is braking the previous functionality we are informing everyone that they may observe such a change and what are the possible ways for the moment.
On the other hand a bug is unexpected behavior that was not intentionally introduced and that is causing the control to behave abnormally.
With all this said, the accessing of columns marked as Visible=False won't be possible for future versions as it was done intentionally to increase the performance of the control. More information on what approaches are supported could be found in this
I hope this information helps to distinguish both terms.
All the best,
the Telerik team
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