I can reproduce this with v1.26.3.1 on Windows7.
And it's even worse than what you describe Erika. You don't even need to attach the object to your avatar. It even happens when you try to edit an unattached object.
Easiest way to reproduce: Create a prim (I made a cube). Set it to flexi. Try to change its size by changing the number in any of the the "Size" fields (don't forget to press Enter). The size-change won't show until you exit Edit-Mode.
Only seems to happen with objects/prims that are flexi.
Oh... another thing... if you zoom in/out considerably while editing, it suddenly displays correctly too. I guess it gets redisplayed when the zoom is big enough to change the LOD.
Henri... i saw your reply while I was writing this... and I think this worked previously. I remember building a flexi-skirt about 9 months ago and back then this used to work. Not sure if the moving worked - as that is still working if the flexi-prims are unlinked - but I think that on resizing it used to display correctly. Is it possibly that the mesh-viewer code from LL introduced this bug?
Anyway, the zoom in/out is a useable workaround.

Henri, as the LOD-change seems to trigger the redisplay, is it possible to add code to the Edit-Mode that automatically triggers this as one moves a prim or changes its size?