Not sure if this is bug,..
-opening two documents
-choose split windows horizontaly
-close tab with the far right ( x ), closeing tabs one by one (to the left ).
-once you arrive at the starting file's tab, clicking the close( x ) button does not work. Double clicking opens a new tab.
I bumped into this with multiple documents open, trying to close the two I was ' splitting/comparing '. I also repeated with *only* two documents.
The top menu close 'close the current' button does close, the last 'split' that fails to close with the ( x ) button.