Reaper v5.980 x64 , Windows 7 x64
Source mode changes when clicking on Region matrix button in render dialog window.
Reproduce by calling render dialog window with some regions defined
Source set to Region render matrix , target autojumps to All project regions
Click on "Region Matrix" button.
Source changes to Selected tracks via master . Bounds remain unchanged.
Sidenote. Rendering, the "estimated time remaining" in source mode
Region render matrix is still assuming I'm rendering all regions, not just the ones I marked in the matrix. Therefore that time estimate is still useless.