# Bug with Block & Lookup: Scope Variable Leak.

GROUPS:
 Rodrigo Murta 9 Votes After debugging a large chunk of code, I could identify this MWE. ClearAll@test test[var_String]:= Block[{association}, association = <|"x"-> <|"key01"-> "ok"|>|>[var]; Lookup[association,"key01",{}] ] If I evaluate: test["x"] test["y"] test["x"] I get an error evaluating the last test["x"]. What is very strange, I expected to find an error just in the evaluation of test["y"].The same error does not occur if we change from Block to Module. In the Block case, we have some sort of unexpected scope leak. Looks like a bug in Lookup.Tested in Mathematica version 11.3Cross post in Stack Exchange