This SM is a bit of a bother...
I have been helping pilots do this one indirectly by shooting all normal mantis I can outside of squad to help them move around while they drop the bombs.
Now the thing is this....
After last Wed update 22 Dec 2010 (which is claimed that it fixed the bombs exploding bug), I have found that this is not true. Having the advantage of watching all the pyros drop and then follow them to the top left and see them go past and DIRECTLY OVER the bombs still they do not explode! Most times they do but not always.
I think the REAL BUG is not that they explode or not BUT RATHER that they do NO DAMAGE WHEN THEY EXPLODE!
Many times I have watched the Pyros go directly over the bombs (and you CAN'T get more accurate then that!!), and have seen the bomb explode in the MIDDLE of the pyros and NOT ONE got damaged at all! I can tell this as there is no flames or smoke from them after the explosion. When the bombs DO some damage they DO show damage even to outside squad pilots.
So I really think this mission needs a closer look than what has been stated has already happened. The main problem is that the bombs don't always seem to do any damage even if the pyros fly directly over them.
It was stated that the positioning is critical for it to work... this may be so but I think the TOLERANCE of placement is a little too fine. I suggest you go and have a look for awhile as pilots are doing the mission and see for yourself that no damage is done to them even if the pyros fly directly over them.