Hi Olaf, Olaf Mersmann wrote:

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It is probably a bug, but it is not likely that it will get fixed soon. \startbackground is an 'old' command, columnsets are 'new' and the interaction is not always perfect.

Is this documented in the manuals and I missed it or simply something one learns with time? If it's not documented, maby it could be posted on contextgarden?

I do not think anything is in the manual, it is one of those situations that grow over time: there are perceived limits in a specific solution (like \startbackgrounds) so Hans writes an alternate subsystem (like \starttextbackgrounds) that slowly becomes powerful enough to take over the original. The documentation is normally not updated until 100% of the old functionality is available in the new subsystem. A page with 'deprecated / outdated' commands on the wiki would certainly be helpful, I agree with that. (CC context dev list) Taco