Joomla - Menu save action overwrites third party changes.

[vmindru]

Steps to reproduce the issue

This video was recorded for Joomla Art as well.
https://youtu.be/XH-dzwYG-oU

1. Amend a submenu in a menu with MegaMenu, add 1 extra column.
2. Open any menu that is part of the "menu" above and just click save.
3. The columns of submenu got overwritten.

Expected result

mm_config settings do not get overwritten

Actual result

mm_config settings :{"rows":[[{"item":157,"width":6},{"item":160,"width":6}]]},"alignsub":"justify"},"item-151":{"sub":{"rows":[[{"item":152,"width":12}]]}}} get's removed

System information (as much as possible)

Joomla: 3.4.3
Purity III: 1.1.5
T3: 2.5.0

Additional comments

[brianteeman]

This is not an issue with the core of Joomla.

[vmindru]

Same issue here: https://www.youtube.com/watch?v=XH-dzwYG-oU megamenu get's overwritten.

[root@srv3 2]# diff v2 v1
17c17

< "mm_config": "{"mainmenu":{"item-101":{"sub":{"rows":[]}}},"mainmenu-cz":{"item-148":{"sub":{"rows":[[{"item":157,"width":6},{"item":160,"width":6}]]},"alignsub":"justify"},"item-151":{"sub":{"rows":[[{"item":152,"width":12}]]}}},"menude":[],"menucz":[],"mainmenu-en":[],"mainmenu-ru":[]}",

"mm_config": "{\"mainmenu\":{\"item-101\":{\"sub\":{\"rows\":[]}}},\"mainmenu-cz\":{\"item-148\":{\"sub\":{\"rows\":[]},\"alignsub\":\"justify\"},\"item-151\":{\"sub\":{\"rows\":[[{\"item\":152,\"width\":12}]]}}},\"menude\":[],\"menucz\":[],\"mainmenu-en\":[],\"mainmenu-ru\":[]}", 

[root@srv3 2]#

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_{This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/7651.}

[vmindru]

ups sorry that was ment for another github ...

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_{This comment was created with the J!Tracker Application at issues.joomla.org/joomla-cms/7651.}