OK, I've managed to duplicate this.
For our reference, this is a step-by-step guide on how to reproduce this bug:
1)
Tools/Options/Text Editor/ActionScript/Formatting Wrapping/Leave Block on single line must be
checked.
2) A block similar to the following must be selected
including a blank line beneath it.
Foo.Define("Foo", { bar:["foo", "bar"], params:{ foo:"Foo" } } );
3) When pasted, the line is truncate to this:
Foo.Define ("Foo",{bar : ["foo", "bar"],
4) Selecting Undo (e.g. Ctrl-Z) restores the complete pasted line.
I've entered this into our tracking system with a link to this thread.
Thanks
Huw