The basis for SPD suggesting charging was neither of the doubts about details of Zimmerman's account. The Serino affidavit transmitted to Wolfinger cites Zimmerman to blame on account of either getting out of his truck (if he hadn't, the event doesn't occur), or, in the alternative, if Zimmerman had explained to Martin that he was a watchman or something like that.
I can't find any evidence for the contention that SPD justified an opinion to charge, using the doubts about the two details NYT reported, or any other inconsistency in Zimmerman's statements.
Trayvon Martin Case Shadowed by Series of Police Missteps - NYTimes.com - Serge F. Kovaleski - May 16, 2012
Bond Hearing of April 20, 2012 [partial] - CNN Transcript
According to this article in the American Thinker,
Tracy Martin was spreading that rumor:
http://www.freerepublic.com/focus/f-news/2878429/posts