H4 I-94 card expiration date error?

[yolanda]

I entered the US in Sept. 2010, 5 months after my husband's arrival. The officer in Detroit Airport gave me an expiration date of 5th Aug.2011 on my I94 form. This expiration date is not consistent with my husband's I94 expiration date (which is in April 2013) or my passport expiration date or my H4 VISA expiration date. I am wondering if this was an error by the officer? If not, what is the possible reason the officer gave me this expiration date? is the expiration date on my I94 (H4) necessarily the same as the one on my husband's (H1B)I94?