Why does FileCount() in the context menu fail to return the correct result?

The test button code is as follows, add it to the 'All Files' context menu and select 'Evaluator Function' function type.
This button works well in the toolbar.

@showif:= all_txt = FileCount("*.txt");selected_txt = FileCount(true,"*.txt");Output(Format("all_txt: %1  selected_txt: %2",all_txt,selected_txt)); return true;
Output("-------------------");
Output("all txt:" + FileCount("*.txt"));
Output("selected txt: " + FileCount(true,"*.txt"));

In @showif, if no txt files are selected, FileCount(true,"*.txt") returns the total number of txt files. If the selected files include txt files, it returns the correct result. FileCount("*.txt") is always correct.

In the main evaluator code, FileCount(true,"*.txt") is always correct, while FileCount("*.txt") is always equal to the former.

Note that I originally wanted to use @showif:=selfiles>0 && FileCount(true,"*.jxl") == selfiles) to display the button when all selected files are jxl. I know I can set the button only for jxl file type, but I want to place it in the "Convert Image" submenu of 'Images' file type.

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