Hi Pawel,
Hi Willi!
After all the solution is simpel ... [...] This command will force the bodyfont and the footnotes font to be the same. If e.g. Myfont is setup as a typeface of Palatino for rm and Helvetica for ss, then the footnotes will be in Palatino when saying \setupfootnotes[bodyfont={small, rm}] and will be typeset in Helvetica when saying \setupfootnotes[bodyfont={small, ss}]
Isn't that logical? But look carrefully on the footnote numbers. Are they also from wanted font? That was my problem. It is not obvious that footnote reference numbers are set with xx size of the bodyfontsize and footnote number with x size of bodyfontsize used in footnote. So the way to set this numbers is to set bodyfontenvironment for both bodyfintsize and 'footnotebodyfontsize'. The puzzle is also that one has no problems since bodyfontsize is default (i.e 12pt). So try to change bodfontsize to i.e.13pt and than look at footnote numbers. If they are correct you are the winner! Thanks for report, Pawe/l