Fluid Value Extraction
There is a difference in accessor detection (method detectAccessor) between:
VariableExtractor detects for ACCESSOR_GETTER by is_callable
StandardVariableProvider detects for ACCESSOR_GETTER by method_exists
This leads to inconsistent variable object handling in fluid when object is using magic method __call, which is detected by is_callable but not by method_exists.
I would recommend to switch StandardVariableProvider ACCESSOR_GETTER detection to is_callable as well.