I could hardly believe I got it wrong, so I tried it in DbVisualiser ... I got 1,4,5,7,8 (just as I thought I would). Could this have something to do with using DbVisualiser (I guess not, since SQL is executed on the server anyway)?

My interpretation is as follows:

This opens a block comment... /*

...so this is not printed PRINT '6'

This is ignored since it is part of the block comment --/*

and it is not the closing of the block comment

This closes the block comment... */

...thanks to which this is printed PRINT '7'

This is an inline comment so it does nothing --*/

This is printed PRINT '8'