The stretcher is attached for example to

• /modules/jcr-tools/apps/jcr-tools/subApps/query/form/tabs/mainTab/fields/statement
• /modules/mail/apps/mail/subApps/verify/formDefinitions/template/tabs/template/fields/data

After clicking the stretcher, the field (area) stretches outside its expected limits, consuming other fields and even the stretcher itself, making it impossible to revert the field size:

We removed the full-screen option from all text-areas in M6 forms (including compatibility ones) on purpose because interaction pattern was quirky anyway. That would call for similarly removing that option ..., even before porting it to new UI FW.