I stand corrected by dkmarsh; AutoFill would tend be the critter responsible for your issue. (I thought of it and immediately forgot about it. )
I've run into a similar issue with AutoFill, but in a much more recent version of Safari than you're running, and although I've now got it functioning properly, I can't begin to tell you what might have corrected my situation. (It seems to me that reinstalling Safari might have helped.)
The new Great Equalizer is the SEND button.
In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire
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