What causes Eclipse to not show FXML file errors until compilation? - eclipse

Question

After installing e(FX)clipse (an eclipse plugin that deals with JavaFX files) the editor works the same way for all files not relating to JavaFX, as to be expected. However, FXML files (which the plugin should help with creation, reading, and editing) do not show errors from eclipse. While it will run properly if all code is correct, it becomes very tedious very fast having to carefully import each class by hand.
After looking through several threads I've found similar problems crop up, with varied solutions.
I have:
1.Used Project> Clean... several times
2.Removed and replaced the project build path
3.Gone through all validation settings for both Java and XML files
4.Checked Problems panel filters to ensure they weren't being hidden in XML files.
5.Checked for missing JavaFX user library.
6.Checked for Project> Build Automatically turned off.
7.Turned Project> Build Automatically on and off.
Say I have this code:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.Insets?>
<?import javafx.scene.layout.GridPane?>
<?import javafx.scene.control.Label?>
<?import javafx.scene.text.Font?>
<?import javafx.scene.control.Button?>
<?import javafx.scene.layout.ColumnConstraints?>
<GridPane xmlns:fx="http:javafx.com/fxml" alignment="center"
Hgap="10" Vgap="10">
<Button text="Button One" GridPane.rowIndex="0"
GridPane.columnIndex="0"></Button>
<Button text="Button Two" GridPane.rowIndex="0"
GridPane.columnIndex="1"></Button>
<Button text="Button Three" GridPane.rowIndex="1"
GridPane.columnIndex="0"></Button>
<Button text="Really extra long button Four" GridPane.rowIndex="3"
GridPane.columnIndex="0" GridPane.columnSpan="2"></Button>
<Button text="Button Five" GridPane.rowIndex="1"
GridPane.columnIndex="1"></Button>
</GridPane>
This should be, and is, errorless.
But once I change it to this:
<?xml version="1.0" encoding="UTF-8"?>
<?import javafx.geometry.Insets
<?import javafx.scene.ll.Label
<?import javafx.sceext.Font
<?import javafx.gnment="center"
Hgap="10" Vgap="10">
<Button text="Button One" GridPane.rowIndex="0"
GridPane.columnIndex="0"></Button>
<Button text="Button Two" GridPane.rowIndex="0"
GridPane.columnIndex="1"></Button>
<Button text="Button Three" GridPane.rowIndex=
<Button text="Really extra long button Four" GridPane.rowIndex="3"
GridPane.columnIndex="0" GridPane.columnSpan="2"></Button>
<Button text="Button Five" GridPane.rowIndex="1"
GridPane.columnIndex="1"></Button>
</GridPane>
Randomly mutilating it, it stays completely errorless until I attempt to run it. If I mess with the code in a more ordered way (to maximize potential errors) the result is the same.
No errors occur on the side of the code (preferred) or in the problems panel.