Hm, too late for to test this, so here are some thoughts:
- raise a ticket at Mendix to make the textbox-OnChange-event behave like an on-change-event. But don’t get your hopes up too high;
Solve it yourself indeed via javascript, that you add to a html-snippet and that starts upon document-ready. Calling a microflow from a javascript is done by calling a nanoflow, which calls that calls the microflow (check if you realy need a microflow, maybe a nanoflow suffices)