Hendon went on holiday last week believing his 27-year-old captain would be signing a new one-year deal at Underhill this week.
But Hendon received a text from Bishop on Thursday admitting he had agreed to sign for Notts County - 24 hours after the East
Midlands club had announced the deal.
"He did not even call me to tell me of his change of mind," Hendon told Barnet's official website.
Bishop, a former England C international, made 95 appearances for Barnet after joining from York and was believed to want to return north.