Let me say otherwise: Why is ObjFPC causing this error.
Mode obfpc raises this error because potential (corner case) ambiguities such as this were one of the reasons for introducing the objfpc mode, part of its raison d'être.
Pascal programmers fall into several camps, one of which sees no need for flagging (or preventing) such potential ambiguities. Delphi's compiler developers are definitely in this camp.
Some of those who develop FPC feel differently, and so introduced a stricter mode.
This is not because the compiler itself has any problems at all with potential ambiguities (genuine ambiguity excepted), being thoroughly deterministic, but because sloppy or careless programming and variable naming style can sooner or later trip up both experienced and rookie programmers.
Some of us need our hand held. Others refuse any such aids, and reuse variable names with apparent impunity.