There are screenshot utilities and some do a pretty good job at capturing the cursor, even if sometime it means a delayed capture (you delay the capture by a few seconds, click the button in the capture utility, hop over to the window where the action is, mimic the action and the screenshot is taken with everything in sight. Note that Gimp comes with its own screenshot capability (File > Create > Screenshot).
For your initial question, my wonder is why are you using that bar brush and not the usual round brush?
For your initial question, my wonder is why are you using that bar brush and not the usual round brush?