NOTE: This concerns the default X cursor set (stored in "/usr/share/fonts/X11/misc/cursor.pcf" or similar). Users who have some cursor theme installed may see different cursors.
JWM uses border cursors that are not consistent between the sides or edges of a window on the one hand, and its corners on the other. See the attached picture "cursors.png" for illustration: it shows the cursors together with their names. For vertical and horizontal side borders, JWM uses the cursors top_side, bottom_side, left_side, and right_side. All of them feature an arrow pointing to a line (the line represents the edge). A set of cursors where an arrow points to a corner is also available in the default X cursor set: top_left_corner, top_right_corner, bottom_left_corner, and bottom_right_corner. Somewhat unexpectedly, JWM does not use these cursors for the corners. Instead, JWM uses a set of cursors that depict a corner without an arrow: ul_angle, ur_angle, ll_angle, and lr_angle. That is a visual inconsistency -- a minor one of course, but still, an unnecessary one. The attached trivial patch "jwm-consistent_cursors.patch" makes the cursor selection more consistent.
PS: In my view, ideally all border cursors should be the familiar double-arrows, a solution that one can see in many third-party cursor themes. But alas the default X cursor set features only horizontal and vertical double arrows, not diagonal ones. So that is not an option.