In a rather large project, but nothing too extraordinary (234 PHP files, 282 Smarty TPL files, 16 JS files, 6 CSS files) I keep getting
PHP0412 Use of unassigned variable ... warnings that pop up in my error list. If I double-click the warning, the file opens and the warnings disappear. Which makes sense because the variables aren't unassigned, the code is correct.
When I close the file, at some time, usually within minutes, the same warning pops up again. It does this for several files. Which means at one time my project has 'only' 10 warnings (all false positive as well) and a little while later I have over 900 warnings because it complains about PHP0412 in dozens of files. I like to keep my warnings list (as) empty (as possible) please.
Code on which it triggers is trivial and usually has an assignment of the variable literally the line above it:
$res = Foo:GetBar();
echo $res; // PHP0412: Use of unassigned variable $res