strange cross-threading ui errors

i'm minute winforms app twin modes: console gui. 3 projects within same solution, console app, ui forms third reason explanation twin interfaces both bond too. console app runs definitely smoothly.

a denote binds user-selections, an ilist<t> where t internal object, step, implements inotifypropertychanged, ui mounted datagridview. glorious during runtime, initial state objects reflected screen.

each step objects assign achieved turn; properties change, being reflected behind ilist upheld datagridview.

this movement ui versions finished formulating backgroundworker lifting events behind ui. step does thing generates stepresult vigilant an enumerated form indicating outcome (e.g. running, notrun, ok, notok, caveat) twine infer summary (because step ran nonetheless definitely expected, i.e. caveat). customarily actions secure database interaction, nonetheless debug mode i incidentally beget result.

if summary null, there's never problem, nonetheless i beget response this:

stepresult returnvalue = new stepresult(stat, "completed caveat")

i an blunder observant datagridview being accessed thread thread combined on. (i'm flitting by tradition handler should hoop invoking mandatory - maybe doesn't?)

then i beget unparalleled response, e.g. controlling futile array r:

stepresult returnvalue = new stepresult(stat, r.tostring());

the actions attain problem, numbers combined purify datagridview.

i'm baffled. i'm presumption it's somehow twine verbatim problem, nonetheless anyone adult clearer explanation?