There appears to be an inconsistency in the implementation of \startparagraph.  When it is used with one argument (or two by my reading of the source) it defines \stopparagraph with a terminal \endgraf, yet with no arguments this is not done. Strangely (to me) it also appears to insert a line-break before \startparagraph[]. The example below demonstrates these issues.

I would expect to have \endgraf inserted with each \stopparagraph regardless of the argument count.

There is also a wiki issue with overloading of the command name \startparagraph. The existing command entry points to the paragraphs mechanism for setting up parallel paragraphs in columns. There is also a \startParagraph command described for the t-pararef module. There is no mention of \startparagraph in the \startsection page, which might be an appropriate place. Perhaps some Wikipedia-style disambiguation mechanism is needed.
\starttext
\startparagraph
One
\stopparagraph
\startparagraph
Twee
\stopparagraph
\startparagraph
Drie
\stopparagraph
\startparagraph[]
One
\stopparagraph
\startparagraph
Twee
\stopparagraph
\startparagraph
Drie
\stopparagraph
\stoptext

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Rik Kabel