Dynamsoft TWAIN Products

I have an OnMouseMove handler on the ActiveX & plugin control that updates a printout with new mouse coordinates.

In IE9, Firefox and Chrome, the OnMouseMove handler is fired correctly while the mouse moves within the surface of the DWT's canvas. This is the expected behavior.

In IE8, the OnMouseMove event seems not to fire (or the handler is not allowed to execute, not sure which) while the mouse is within the region of the surface of the DWT's canvas. Then, when the mouse leaves that region, the events that should have been raised/handled earlier are suddenly released and/or handled all at once.

The "printout with new mouse coordinates" is a <div /> next to the DWT that is prepended with a new line of text. Upon each event, it adds the text "[Event] on image 0 at ([X], [Y])" to the top of this div. The code is as follows, just to be extra clear:
But really, I don't understand how this could be a DWT issue: Another event, OnMouseClick, does NOT suffer from the same delays UNLESS the OnMouseMove handler not only exists, but actually adds to the printout. That is, if the printout line is present in the OnMouseMove event handler, then the OnMouseClicks are also held up; if the printout line is removed (but the empty OnMouseMove handler remains) then the OnMouseClicks are not held. So the event must be held up in the browser, since it depends on not whether it is handled, but the manner in which it is handled. But equally puzzling is what would be different about these two handlers that would cause this difference - and only in IE8?

Has this been seen before?

By throttling the events in javascript to only interact with the UI from OnMouseMove at most every, say, 200 milliseconds, the problem seems to go away.

Perhaps IE 8 just gets overwhelmed with UI updates.

(I consider this issue closed)

I'm glad to hear that you solved the problem by yourself.