Set width & height in FormItem cause system freeze

Steps to reproduce:
1. This code hangs: (I put this in a Tab Navigator)

<mx:HBox width="100%" height="12%">
<mx:FormItem label="No." required="true" width="15%" height="100%">
<input:BaseTextInput id="line_no" text="

{myRfqLine.number}" enabled="{!myRFQLinesForm.isReadOnly}" change="myRFQLinesForm.handleTextChangeEvent(event);" width="100"/>
</mx:FormItem>
<mx:FormItem label="Revision" width="15%" height="100%">
<input:BaseTextInput id="line_rev" text="{myRfqLine.revision}" enabled="{!myRFQLinesForm.isReadOnly}" change="myRFQLinesForm.handleTextChangeEvent(event);" width="80"/>
</mx:FormItem>
<mx:FormItem label="Description" width="40%" height="100%">
<input:BaseTextInput id="line_desc" text="{myRfqLine.description}" enabled="{!myRFQLinesForm.isReadOnly}" change="myRFQLinesForm.handleTextChangeEvent(event);" />
</mx:FormItem>

<mx:Button id="attachPartButton" label="Attach" click="partAttachClick()" enabled="{!myRFQLinesForm.isReadOnly}" styleName="basicButton" labelPlacement="right" icon="@Embed(source='/assets/images/add.png')"/>
</mx:HBox>

2.



3.

Actual Results: Freezed


Expected Results: No hang

Workaround (if any):

I modified it to this one and it works well: (removed 'required=true' and width & height in FormItem tags)

<mx:HBox width="100%" height="12%">
<mx:FormItem label="No.">
<input:BaseTextInput id="line_no" text="{myRfqLine.number}

"/>
</mx:FormItem>
<mx:FormItem label="Revision">
<input:BaseTextInput id="line_rev" text="

{myRfqLine.revision}

"/>
</mx:FormItem>
<mx:FormItem label="Description">
<input:BaseTextInput id="line_desc" text="

{myRfqLine.description}

"/>
</mx:FormItem>

<mx:Button id="attachPartButton" label="Attach" click="partAttachClick()" enabled="

{!myRFQLinesForm.isReadOnly}

" styleName="basicButton" labelPlacement="right" icon="@Embed(source='/assets/images/add.png')"/>
</mx:HBox>