problem with deformation of curve modifier i was want to make cylinder with holes i make this plane 
and then i add array and curve modifier as shown :

you can see the mesh is not connected even when merge is enabled
so i apply the array modifier and then merge them manually in edit mode
but the problem when i want to change the size of the mesh by scale the curve
the merged vertices that i connected them (merge) deformed in strange way unlike other vertices    :

so i know it should scale before apply array but i just want to know why this happen  it just  a merge ??
It's all about the order of events.

'First and Last' merging in the Array modifier doesn't work because the Curve hasn't happened yet. (It's only really useful when the rotation is performed in the array)
Modifiers operate on the mesh as handed to them by the stack. But edits on the mesh happen before any modifiers. So you have merged vertices on the strip in its uncurled state. If you switch off the Curve modifier, you can see:


One way of merging the ends of a cyclically-deformed array is to put a Weld modifier below the Curve. Then you can leave all your modifiers live.