Kerbal Space Program

Repro steps:
1. Load the craft file attached (Hellbat d test.craft).
2. Click on the upper of the two Mk1 fuel tanks (with all the jet engines below). This is quick.
3. Click on the parts tab to delete your selection. KSP hangs.

It's possible that it completes eventually, but I didn't have the patience; I force-quit after a minutes or two in various attempts.

Workaround: delete it in three pieces.
1. Load the craft file.
2. Click on one of the 8-way symmetric decouplers that defines the last stage. Delete it; this is quick.
3. Click on one of the 8-way symmetric cube struts closest in to the Mk1 fuel tank. Delete it; this takes a second or two.
4. Click on the upper of the Mk1 fuel tanks. Delete it; this takes a second or two.

My wild guess is that it's some quadratic-time operation to do with deleting struts.