See subject. Testing was with IE11 and github version of Wt 3.3.3-22-g00f113f. This may be the same issue reported in #2604, although IE11 was used here instead of IE9.
A test case illustrating the issue is attached; it is just a slight modification to the hidden.cc test case attached to #2604.
I've also attached a one line patch that seems to help. The patch has only had limited testing.