I have had similar issues between lucent and netgear, where the
presence of a lucent card broke an IBSS netgear network.  My take is
that IBSS mode doesn't really work in some cards.

I have also seen some cards fail to do speed negotiation correctly.
In an IBSS network with 2 Mb/s cards, with the IBSS created by one of
them, a Lucent 11 MB/s card correctly works (transmits at 2 Mb/s, the
supported speed of the IBSS from the beacon).  But the IBM T30
internal 802.11b (Intersil version) seems to send at 11 Mb/s anyway,
even though it picks up the IBSS SSID (1.6-stable).  It can
communicate with the lucent 11 Mb/s card, but not the 2 Mb/s cards.
Attempts to set the speed manually to 2 Mb/s also seem not to work;
commanded speed shows up correctly in wiconfig but actual seems to hop
back to automatic.

I have not seen any of this wierdness with real APs, but I also have
only used 802.11b APs, never an 802.11 2 Mb/s DSSS AP.

        Greg Troxel <gdt@ir.bbn.com>