When you merge records and those records have constituencies, the system does merge them; however, the end date on the merged constituencies is flawed.
The start date will take the first date on any of the merged constituent records (good)
The end date, if one of the constituent records show a blank end date, will leave the field blank, even if a constituent record being merged has an end date.
A better idea would allow this item to be configurable... do you want the field to be left blank if any of the constituent records show a blank end date OR do you want to add a the latest reported end date, if any of the constituent records being merged has an end date reported?
Right now, after a merge, we'll need to go back and end date all the constituencies... not fun.