problems with lambda ZAP

[bgottgens at molbiol.ox.ac.uk]

Hi everybody!
Has anybody out there encountered a problem with the EcoRI site in the 
Stratagene lambda ZAP cDNA cloning system.
We found that in 50% of the clones that we sequenced one A is missing in the 
EcoRI site. We have complained to Stratagene about this, because it is a bit 
of a nuisance, loosing such a nice site as Eco for recovering the inserts, but 
alas, they were not very helpful.
Has anybody any idea how this can have happened in different clones.
My feeling is that it is because of a kit component.
Any comments welcome.
berthold
e-mail address: bgottgens at molbiol.ox.ac.uk