There're two ideas I have. First, since your symptoms are consistent with "COMMAND-CLICK" (or even COMMAND-MENU-ITEM, which I'll bet you never tried !!!) then this could mean either your macro or your mouse is holding the CTRL button for some reason when the menu command is selected. Try this - replace the Menu command with "Type a Keystroke" using "COMMAND-[" (which is the Safari shortcut for that menu item) as the key instead. If this fixes it, we have another clue. It will probably work around your problem, if nothing else.
Another idea I have, which I didn't want to test earlier, is whether this command is running both your macro and the button at the same time. (Some people call this "not eating your keystroke" or in this case, mouse click.) One way to test this is to turn off your macro, then press the mouse button to see what happens. If nothing happens, this isn't the cause of the problem. But if something happens, we have a new clue. I still don't want to test this because my mouse is likely a different model than yours, so testing my mouse doesn't necessarily fix your problem.
I feel like I'm only 70% likely to be able to solve your problem. But that's better than 0%.
P.S. I always love using the word "There're." It's so hilarious. It makes me sound like a pirate.