Why did US debt increase during 1998 - 2001 budget surplus? Why did debt remain exactly the same during 2013 summer deficits?

A Trillion Dollar [$959 Billion] Budget Contradiction?

Between 1998 and 2001 the US had a budget surplus of $558 billion ($69, 125, 236 & 128 billion respectively).

Between 1998 and 2001 the US federal debt increased by $401 billion ($109, 128, 23 & 141 billion respectively).

1998 surplus of $69 B increased debt $109 B
1999 surplus of $125 B increased debt $128 B
2000 surplus of $236 B increased debt $23 B
2001 surplus of $128 B increased debt $141 B
-published US Treasury figures

**CBO:  Deficit increases $146 Billion in August 2013
Treasury:  Debt increases $0 in August 2013

**US Federal Government Ran $98 Billion Deficit in July 2013 -- But Debt Stayed Exactly $16,699,396,000,000 - just $25,000,000 below the legal limit allowed by the debt ceiling.

**From May 17 to October 16, 2013 (150 days) the US debt has remained at $16,699,396,000,000

**On October 17, 2013, the day after the debt ceiling is raised, the debt jumps $328 Billion to $17.075 Trillion.

**"Why is the debt clock stuck while deficits are increasing?"

"Because, outside the 3 1/2 months there was no debt ceiling, we’ve been at said debt ceiling since mid-December. The Treasury has been able to get away with deficit spending by “underfunding” the federal employees’ retirement funds (that is, instead of first buying Treasury securities with the excess money and then spending it, it has just been spending it and keeping an off-the-books record of what has to be replaced) and drawing down the cash on hand." 
-Hot Air commenter Steve Eggleston

Among the “extraordinary measures” Treasury Sec. Lew said he could take to create this “headroom” under the debt limit were:
1) not investing new money from the Civil Service Retirement and Disability Fund (CSRDF) in U.S. Treasury securities, which he said would create $6.4 billion in “headroom” per month
2) not reinvesting $58 billion in Treasury Securities held by the CSRDF that would be maturing and not reinvesting $16 billion in interest owed to the fund, which would create $74 billion in headroom
3) suspending the routine daily reinvestment of $160 billion in special Treasury securities held by the Federal Employees’ Retirement System Thrift Savings Plan, which would create another $160 billion in headroom
4) suspending the routine daily reinvestment of Treasury securities held by the government’s own Exchange Stabilization Fund, which would create another $23 billion in headroom

What missing variable accounts for the disparity?

"The national debt increase during a given year is not the same as the "total budget" deficit commonly reported, due to a variety of accounting complexities involved. These differences can make it more challenging to determine how much the government actually spends relative to tax revenues. The increase in the national debt during a given year is a helpful measure to determine this amount."
-Wikipedia