[Zope] External method called twice?

[Francesco Chicchiriccò]

Hi,
I'm in trouble with zope and external methods.

Sometimes (and I haven't been able to detect exactly when), my external
method get called twice, even thought it is called only once from ZPT. It
seems there are two independent threads accessing the same method's body.
Any suggestion? Something like Java's 'synchronize'?

Could someone out there help me?
Thanks in advance for your patience.