JNF UK has parted company with its new chief executive after just a few months in office, the second head to go in two years.
Elliot Conway, who joined after a lengthy search by the charity for a chief executive following the acrimonious departure of his predecessor, left on Wednesday.
The JC has also learned that a senior employee, Hilary Cane, who runs JNF's multi-million pound charity voucher scheme, has been suspended.
But JNF UK chairman Samuel Hayek played down the developments, insisting that there was "absolutely no ongoing instability or uncertainty" at the charity, whose honorary patrons include Prime Minister David Cameron as well as Gordon Brown and Tony Blair.
Mr Hayek, explaining that Mr Conway had recently completed a six-month "trial period", stated: "As sometimes happens at the end of such probationary periods, it was decided not to move to a full-time appointment."
Mr Conway, 31, was unavailable for comment. Formerly the president of Cambridge University Jewish society and director of the Parliamentary Committee against Antisemitism, he was recruited by JNF more than a year after the chief executive's post was first advertised.
But one recently appointed member of the charity's board, Baroness Deech, said on Tuesday that she had "heard nothing from JNF" about Mr Conway's departure.
Mr Hayek said that Mrs Cane had been suspended as manager of KKL Charity Accounts on "a technical matter", adding that it "does not affect KKL's daily activities and KKL Charity Accounts are in excellent health".
Mrs Cane said she could not comment.
Mr Hayek became chairman of the JNF early in 2008 in order to settle the charity's bitter dispute with its Israeli associate Keren Kayemet L'Yisrael which had cost the two organisations an estimated £4 million in legal fees between them.
The president of JNF, Gail Seal, stepped down shortly afterwards, followed by the charity's chief executive Simon Winters. He sued the charity for constructive dismissal but dropped his claim last year.
Mr Hayek - who reported last autumn that the charity's "recent turbulent times" were behind it - stressed again this week that "the troubles of the previous administration are very much over". The charity, he said, was "completely focused on its key mission of bringing life" to the Negev region in southern Israel.
But some fallout remains from the conflict with Keren Kayemet. The JNF has sued one of its former board members, Charlie Sherling, for nearly £700,000, which it claims he owes
in contributions towards its legal expenses.
According to the JNF's last available accounts for 2008, it recorded an income of £15.6 million, making it British Jewry's third largest fundraising charity.
Around of half of that figure, £7.6 million, derived from KKL Charity Accounts, the voucher scheme which channels donations to other UK charities. Some £800,000 was contributed by satellite charities such as One Family, which has recently disaffiliated from JNF.
Andrew Alexander, director of One Family, which raises money for victims of terror in Israel, said that while JNF had helped it to start, it was "always our intention to leave JNF".
Mr Hayek said JNF had "amicably disengaged" from One Family, explaining that JNF was "slowly reducing" involvement with causes that did not fit within the "traditional ambit" of the charity's work.
He said that JNF's income for 2009, according to draft accounts now in preparation, would be "in line" with the previous year, alongside a drop in expenditure.
The charity has further cut costs this year by closing regional offices in Manchester, Liverpool and Leeds although Mr Hayek said a Manchester office would reopen "in due course".
The Glasgow-based JNF KKL Scotland operates as a separate charity. Its chairman Stanley Lovatt said: "We became independent of JNF UK three years ago and I am delighted that we did."