different arrData between create and save - isAttributeSet get not the same returns

[zonky2]

Checklist before I submit this issue report

I confirm that:

• I have tested this with the latest version available
• I have read documentation @ http://metamodels.readthedocs.org/en/ or http://metamodels.readthedocs.org/de/
• I have checked the Contao community forums for references https://community.contao.org/
• I have checked existing issues for duplicates and found none @ https://github.com/MetaModels/core/issues?q=is%3Aissue

My environment is:

(Please fill in the actual values from your environment)

Key	Value	Comments
PHP version:	5.6
Contao version:	3.5.27
MetaModels version:	core master (a15)
Installation via composer:	yes
Installed MetaModels packages:	bundle_all
DCG version:	master (b39)

Steps to reproduce

1. create attribute Alias with allwaysSave
2. create input mask with readonly
3. create and save items

look at contao-community-alliance/dc-general#350

at the "first save" (create) we doesn´t create the alias - we create the alias with the "second save" (update)

the MetaModels.php call the method modelSaved if is isAttributeSet true

core/src/MetaModels/MetaModel.php

Line 1035 in 08b5022

if ($objItem->isAttributeSet($objAttribute->getColName())) {

but at Item.php

core/src/MetaModels/Item.php

Line 245 in 08b5022

return array_key_exists($strAttributeName, $this->arrData);

we have different keys at array $this->arrData between create e.g.

Array (     [name] => a8     [vorname] => b8     [published] => 1     [tstamp] => 1496848172     [id] => 10 )

and update e.g.

Array (     [id] => 10     [pid] => 0     [sorting] => 0     [tstamp] => 1496848200     [name] => a8     [vorname] => b8     [email] =>      [published] => 1     [abteilung] =>      [alias] =>  )