I did some experimenting with recordings from my 1197 ...
On my 1st attempt to make a sub-recording, I clicked the start point and end point of the sub-recording in the SI image pane ... This sub-recording failed to reload into Humviewer like you described ...
I then closed Humviewer and deleted the sub-recording files created so I could start from scratch again ...
On my 2nd attempt to make a sub-recording, I clicked the start point and end point of the sub-recording in the 2d image pane ... This sub-recording loaded successfully into Humviewer ...
Now with every attempt to make a sub-recording, I can click the start point and end point of the sub-recording in either image pane (2d or SI) and the sub-recording will successfully load into Humviewer ...
Rickie