Mr Seamus Mallon's resignation as deputy first minister designate last July is being cited as a second potentially significant obstacle to the creation of Northern Ireland's power-sharing executive.
Even if Sinn Fein and the Ulster Unionists could conclude a deal to break the impasse on devolution and decommissioning this week, there is a serious question mark over Mr David Trimble's ability to command sufficient votes to secure his re-election, and that of Mr Mallon or some alternative deputy first minister, in accordance with the rules of the Northern Ireland Assembly.
A fresh election became necessary under the rules when Mr Mallon resigned on July 15th in protest at Mr Trimble's refusal to bring the executive into being.
The renewed focus on the Assembly arithmetic comes as the key parties permit some cautious optimism that their present "serious engagement" could deliver a positive result for the Mitchell Review.
Both men were elected on a joint ticket after the Assembly elections last year by securing an absolute majority of the votes of those designated "unionist" and "nationalist" Assembly members.
However, with the UUP's North Down Assembly Member, Mr Peter Weir, firmly in the anti-agreement camp, the 58 designated unionists at Stormont are split 29/29 for and against the Agreement. That would leave Mr Trimble one short of the absolute majority he and a new deputy first minister would require in a second election.
A second election would have to take place following any agreement to reconvene the Assembly to trigger the d'Hondt procedure for the appointment of ministers. In those circumstances, a decision by one of the two members of the Women's Coalition to re-designate herself a unionist might be enough to carry the day.
However, well-placed sources anticipate that should Mr Trimble agree to form the executive in what might prove controversial circumstances - specifically, circumstances involving some departure from his declared position on decommissioning - he could face defections.
Should that happen, the Alliance Party members (six, including Presiding Officer Lord Alderdice) could find themselves with a critical role in determining the fate of the Belfast Agreement.
Both governments have been aware of this potential problem since the moment of Mr Mallon's resignation. At the time - courtesy of some apparent ambiguity in the Assembly's Standing Orders - a question was raised about the legal standing of the resignation, and the requirement for a second election, in the pre-devolution period.
The Northern Ireland Office, however, had no doubt about the issue, and moved promptly to stop Mr Mallon's ministerial salary. Moreover, sources close to the deputy SDLP leader have made it clear that, if he returns to the post, "it will be by the front door, not the back."