Field ack is usually greatly reduced in FSO. Well, unless you me.
As for the mass disco: large bomber formations seem to bread weirdness in the SEA. Once at practice for a large raid we were using the "all drop on lead's mark" carpet bombing method. When the GL keyed up everyone else had a 4 second screen freeze and missed.
Another time someone found that airshow smoke was enabled. Half of us went poof.
1st suspect is a sound issue. Since it unlikely that you all use the same custom sound it may be the default and therefore a bug(HTC not responsible for custom sound issues). Or another thought. Are you all using an outside VOX server. Or were all of you filming?
If any where filming, might want to send it to HT.
At any rate AFAIK it is often difficult to reproduce such occurrences. Just watch your step the next time your in a large 234 raid in FSO(never say never)