I think it's fine/tolerated, a simplification from the full/stricter: It was only after I closed the door that I remembered (that) I had forgotten the keys. The final relative ("that") in this one above allows a tense simplification in the subordinate after it ( I had forgotten-> I forgot, past perfect-> simple perfect, see Swan) after it and it may be eliminated itself without loss of clarity. res=FA0617FE3F550C728EDDAA0894DC404482 ...
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