TYPO3 Core

Are you talking about a default sorting, such like alphabetically by title or date, or is it about a manual sorting using up-/down-buttons?
The both tables (entities) should be sorted as defined if you look at them stand-alone. I guess your sorting issue concerns the MM-relation, so if your inside table1 and manage relations to table2? Did I get this right?

I was talking about default sorting indeed of the table 2. When in MM-relations it does not inherent the default sorting of its own table definition.

You can set the ordering of the child table in the TCA array, using ext_tables.php. It could be an extra feature to the kickstarter though to either set a default sorting for when the table is used in the MM-relationship. If not, I would change the default setting from uid to the selected default for the table itself. Just a minor issue.

Okay, I can confirm this as a feature request for TYPO3 4.2.

t3lib_loadDBgroup::readMM() currently doesn't provide a possibility to use a default sorting by the fields defined in $TCA[<table>]['ctrl']['default_sortby']. Tables that are used for storing MM-relations have the fields sorting and sorting_foreign by default. Also the widgets in TCEform, that present the selector-boxes, have to be changed to hide the manual sorting buttons.

To enable the default sorting, I could imagine the following:
$TCA[<table>]['columns'][<field>]['config'] = array(
'type' => 'select',
'MM' => 1,
'default_sortby' => 1
);
Just to set the property "default_sortby" to a true value. Thus the manual sorting will be ignored in t3lib_loadDBgroup::readMM() and TCEforms will hide the sorting buttons, as mentioned above.