Hi Andreas,
The reason I was looking at custom controls was because of my confusion about the hidden aggregation of layoutData that gets added to your control automatically but obviously in your namespace.
e.g. I didn't realise that <f:SimpleForm> should be followed up by <f:layoutData> and not <layoutData>.
Anyway, standard control gone now (except for my extension of CustomTile for the TileContainer on the right).
BTW - Having the OpenUI5 source cloned locally makes investigating these things so much easier (not to mention making it easy to see which controls have extension points if you do need to do something unique without rewriting a control)!
Cheers,
Matt