So far, overhang mandates in the minimum 400 (1949) to 656 (1990, 1994, 1998) seat Bundestag have been rare, though more common lately:

2005. 16
      
2002. 5(+2)
      
1998. 13
      
1994. 16
      
1990. 6
      
1987. 0
      
1983. 2
      
1980. 1
      

1976, 1972, 1969, 1965: 0

1961. 5
      
1957. 3
      
1953. 2
      
1949. 2

Obviously, overhang mandates are likely when even the largest party is well below 50%, that is, when there are numerous parliamentary parties. With the PDS in East Germany, overhang mandates became much more likely (and as you can see, when they failed on the 5% in 2002, overhangs were temporarily reduced).

Overhang mandate melting would count as real problem only when the government majority is hair-thin.

I note that in the diary I simplified the system. In truth even the seats apportitioned for the individual states ars not fixed: there is a compensation system between the states, primarily with the aim to shuffle fraction votes. This can reduce overhangs. (And then there is the 5% limit, and rules for parties under 5% with direct mandates, and the fraction rounding that reduces the minimum number of seats...)

_{*Lunatic*, n.
One whose delusions are out of fashion.}