Using center_x produces a crash

Setting center_x to "true" in an XML layout produces the following crash:

Invalid call
Called from flixel.ui.FlxTypedButton::set_x line 585
Called from flixel.addons.ui.FlxUITypedButton::set_x line 1147
Called from flixel.addons.ui.FlxUI::_loadPosition line 4970
Called from flixel.addons.ui.FlxUI::_loadSub line 989
Called from flixel.addons.ui.FlxUI::load line 886
Called from flixel.addons.ui.FlxUIState::loadUIFromData line 388
Called from flixel.addons.ui.FlxUIState::create line 190
Called from states.CreditsState::create line 26
Called from flixel.FlxGame::switchState line 649
Called from flixel.FlxGame::update line 739
Called from flixel.FlxGame::step line 689
Called from flixel.FlxGame::onEnterFrame line 554
Called from openfl._legacy.events.EventDispatcher::dispatchEvent line 98
Called from openfl._legacy.display.DisplayObject::__dispatchEvent line 182
Called from openfl._legacy.display.DisplayObject::__broadcast line 161
Called from openfl._legacy.display.DisplayObjectContainer::__broadcast line 286
Called from openfl._legacy.display.Stage::__render line 1103
Called from openfl._legacy.display.Stage::__checkRender line 351
Called from openfl._legacy.display.Stage::__pollTimers line 1084
Called from openfl._legacy.display.Stage::__doProcessStageEvent line 430

Version info:
Haxe: 3.4.2
HaxeFlixel: 4.2.1
Flixel-UI: 2.2.0

Possible workaround: Using

center_on_x="screen"

does the trick.

Start at FlxUI::_loadPosition, where the XML center_x value is processed, and trace the set_x calls in FlxTypedButton and FlxUITypedButton. Reproduce the crash with center_x="true" and compare it with center_on_x="screen". Done means center_x="true" loads the layout without an invalid call and centers the control on the x axis.