Rule commonExpr was fixed, so this issue went away.
https://tools.oasis-open.org/version-control/browse/wsvn/odata/trunk/spec/ABNF/odata-abnf-construction-rules-v1.0-wd01.txt?rev=58
https://tools.oasis-open.org/version-control/browse/wsvn/odata/trunk/spec/ABNF/odata-abnf-testcases.xml?rev=58
The rule for $filter delegates to boolCommonExpr which doesn't resolve to simple property names, so
$filter=Name eq 'Hugo'
is illegal. Root cause is the broken rule for commonExpr.