Hiding column selection containing two hidden regions results in incorrect hidden regions

With the example feredoxin alignment:
1. Hide column 50-60, and 70-80.
2. Hide columns 49-81 (should just contain both hidden column markers)

Note that a new blue triangle will appear between 36 and 37, and hidden region now extends to 92 (column 93 is visible).

Exporting jalview annotations shows that the hidden regions list is corrupt:
JALVIEW_ANNOTATION
# Created: Wed Jan 04 14:19:58 GMT 2017

VIEW_HIDECOLS 48-80,69-79

Expected behaviour is that only one hidden region should remain, extending from column 49 to 81.