Error: Attempt to evaluate a block that is already being evaluated

I am using a block as a parameter in a recursive function, and get this error. 
Does this have to do with blocks as not-quite-full closures? If so, any 
workarounds?

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The workaround is

  aBlock reentrant value

This non-reentrancy issue is orthogonal to what #fixTemps works around (well, 
almost).