[KevinH]

Well dragging and dropping tabs while selecting them on my MacBook works perfectly. I have clicked on and dragged the tabs repeatedly with no problems.

So perhaps it is just memory corruption from some earlier Qt/Sigil code running.

Please try to make it crash again with a copy of an epub and capture the full cash report. If the backtrace of the crashing thread is different, then it points to memory corruption which can be very hard to track down.