1) Do you use the standard editor of dokuwiki or ckgedit (there were some issues with the latter as far as I remember)
First, I'm not aware of this, which doesn't mean that it wasn't at some time reported, but almost always when someone reports such an issue I try to address it quickly. So either it wasn't reported in quite this way, or in the particular instance/configuration wasn't fixable and your problem could be one of those. There have been cases with ckgedit where a blank page occurred, but I believe they have been addressed.
As to the current problem: With Internet Explorer 11, you can set the document and/or browser mode (compatibility settings), so try different settings. Click F-12 to get the developer tools and it should give you the various options.
The simpler route is to use the compatibility settings in the tools menu, but it doesn't give you any control.