When a GuiObject has AutomaticSize set to anything but None, the automatically sized axis will no longer respect any bounds described by UISizeContraint.
In the provided footage, a reference frame that is 200 pixels tall with no automatic size enabled (red) is compared with another frame with automatic size enabled on the y-axis (green). When the 50 pixel frame is duplicated, the red frame resizes as intended. However, the size of the frame goes beyond the bounds specified by the UISizeContraint.
Expected behavior
The red frame will resize up to the maximum specified by the UISizeContraint.