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If I am understanding the situation correctly, European mortgage covered bonds are similar to U.S. mortgage backed securities (MBS). Trading was stopped because:
....."We are in a deteriorating situation,'' Patrick Amat, chairman of the Brussels-based [European Covered Bond Council], said in a telephone interview. "A single sale can be like a hot potato. If repeated, this can lead to an unacceptable spread widening and you end up with an absurd situation."...
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Translation - We can't sell these bonds because the real market value of these bonds will then be established and the "absurd situation" of devaluing these bonds from their fantasy "mark to model" values will occur.
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From Calculated Risk:
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