I'll check the physical charts later, but the VASSAL Chart indicates ignore 1 flag at Full Strength, and the C&C.net webiste also has this.
So I believe LBCH ignore 1 flag at Full Strength
I updated this rule for LBCH on Vassal charts earlier this year to bring them into line with the main rulebook (which I assume is where website info came from). In 4th edition main rules, I found the rule mentioned in the combat section, paired with the same about Warriors.
The rule is not mentioned in the detailed description of LBCH (Exp 2 rules, 2014 printing), which might explain why it didn't make it to the player aid either.
It seems to me that these guys are warriors on wheels, so it makes sense that they have the full strength rule. Another indication that we should go by the main rule-book is scenario 410 (
Mons Graupius
) - that scenario is set up such that two LBCH are unsupported and in range of bow units, one with an obstructed retreat path. This seems reasonable only if the LBCH is initially able to ignore a flag.