You're probably right, but here's what perplexes me:
The RB may not have originally intended WP during the MPh at all. C8.6 only says that WP can be fired "in any friendly
fire phase." Arguably, the MPh is not a "fire phase" except that a Q&A allows WP to be used then:
A8.1 & C8.6 May a Gun fire WP during DFF (is DFF considered a friendly fire phase – C8.6?)?
A. Yes, provided no other non-WP DFF has occurred; C8.6. {1}
Fair enough, but the reason this is acceptable is because a DEFENDER's units may fire in the MPh
and in the DFPh without violating the "only fire in one phase" rule (A.15 and A7.1).
So if the MPh and DFPh are being treated as ONE fire phase, then once non-SMOKE fires in
either phase, your SMOKE potential would be voided.
I am not sure if folks play this way, but to do otherwise creates a double standard.