Toad does not format nested comments in the form of /* … */ correctly. It executes them correctly (i.e. no result set is returned), but it fails to color the code correctly.
Note how the “SELECT * FROM t;” isn’t green like the rest of the comments, and even the final */ is gray and not green. In MS Management Studio the entire section is green, as in:
Pressing F5 just repeats the entire text into the Messages tab, with no result set returned, which is correct behavior. But Toad’s lack of proper formatting can be very confusing. It’s particularly difficult when trying to debug a long piece of code by commenting sections out: you can’t easily tell which sections are commented out because the colors have not changed.