I seemed to have discovered a bug in MFC 4.21 in the CSliderCtrl class. SetSelection(int min, int max) is a function that shows a horizontal line inside the slider bar. Its two arguments respectively set the starting and ending position on the line.

This function works fine until I enter -1 for the minimum, at which time it uses the maximum value for both the maximum and the minimum. This causes no line to be shown.

If anyone knows a solution to this, or a creative way to get around it, let me know !