System information (version)

• OpenCV => 4.0.0
• Operating System / Platform => Windows 10 64 Bit
• Compiler => Visual Studio 2017

Detailed description

unknown file: error: C++ exception with description "OpenCV(4.0.0) d:\opencv\opencv-4.0.0\modules\core\src\matrix.cpp:169: error: (-215:Assertion failed) u->refcount == 0 in function 'cv::StdMatAllocator::deallocate' " thrown in the test body.

Steps to reproduce

cv::ocl::setUseOpenCL(false);
UMat foo( 10, 10, CV_32FC1 );
cv::resize(foo, foo, cv::Size(), .5, .5 );  // <-- happens here

Only happens when src==dst for cv::resize
See similar: #8693