Im using 2.0.5 SDL2. When i set window to be opengl, borderless AND non-resizable, i no longer receive enter/leave event when dragging pressed mouse. In order to fix that i must add resizable flag. I checked my own code and couldnt find a clue if my own code interfere with SDL but i seriously doubt it since i must just add resizable flag to fix behavior.
Basically i wanted to create plain window without ANY decorations (borderless is not enough because that thing still leave some small but trash & unusable decors). So im forced to use borderless+nonresizable flags and recreate all window events (which i hate but i guess currently there is no way around if i want to create clean window in portable fashion).