QGIS Dissolve tool re-projects and rotates layer

I'm trying to use QGIS to aggregate polygons according to an ID attribute.

I'm using the shapefile of school district polygons in Michigan found here:

http://ift.tt/1yhejnf

MI Geographic Framework School Districts (v14a) is the name of the shapefile I'm working with.

I'm trying to create a shapefile of Intermediate School Districts, which in Michigan are a level of aggregation above school districts.

I should be able to do this using the dissolve tool, as there is an ID variable in the v14a shapefile (called ISD).

However, upon doing so, the resulting polygon layer appears to have been re-projected and rotated.

Here's the input polygons:

And here's the result of the dissolve:

Any idea what's going on here??

I would be particularly grateful if there was a way to reproject the rotated layer so as to undo the rotation, as I had already done a fair amount of stuff by hand to add new attributes to the merged layer (so that starting from scratch would require a lot of repeated manual labor).